Child psychologist Catherine Deane is hired to conduct an experimental virtual reality treatment for coma patients: a "Neurological Cartography and Synaptic Transfer System" device managed by doctors Henry West and Miriam Kent that allows her to enter a comatose mind and attempt to coax them into consciousness. The technology is funded by the parents of her patient, Edward Baines, a young boy left comatose by a viral infection that causes an unusual form of schizophrenia. Baines's progress has been hampered by a bogeyman -like alter ego whom Deane avoids. Despite Deane's lack of progress, West and Kent reject Deane's suggestion to reverse the feed to bring Baines into her mind, fearing the consequences of his experiencing an unfamiliar world. Serial killer Carl Rudolph Stargher traps his victims in a cell-like glass enclosure that slowly fills with water by means of an automatic timer, then uses a hoist in his basement to suspend himself above their bodies while watching the recorded video of their deaths. He succumbs to the same schizophrenic illness and falls into a coma just as the FBI identifies him, leaving them without any leads as to the location of his latest victim, Julia Hickson. After learning of this experimental technology, Agent Peter Novak persuades Deane to enter Stargher's mind and discover Hickson's location. Deane enters the dark dreamscape of Stargher's twisted psyche, filled with doll-like versions of his victims. Stargher's innocent side manifests as Young Stargher and leads Deane through his memories of abuse he suffered at the hands of his sadistic father. Deane nurtures Young Stargher in hopes of obtaining Hickson's location, but she is thwarted by another manifestation: King Stargher, a demonic idealization of his murderous side that dominates the dreamscape. King Stargher torments Deane until she forgets the world is not real. Dr. West discovers this while monitoring Deane's vitals. He warns that what happens to Deane while she is integrated into Stargher's mindscape will inflict neurological damage on her real body. Novak volunteers to enter Stargher's mind to make Deane remember herself. Inside Stargher's mind, Novak is captured and subjected to King Stargher's torture while Deane looks on as Stargher's servant. Novak reminds Deane of a painful memory of her younger brother who died after a six-month coma due to a car accident during her college years to reawaken her awareness that she is in Stargher's mind. Deane breaks free of Stargher's hold and stabs King Stargher to free Novak. During their escape, Novak sees a version of the glass enclosure with the same insignia as the hoist in Stargher's basement. Novak's team discovers that after the hoist's previous owner went bankrupt, the government hired Stargher to seal up his property in rural Bakersfield. Novak races to the property and finds Hickson treading water in the enclosure and breathing through a pipe. Novak breaks the glass wall and rescues Hickson. Deane, now sympathetic to Young Stargher, locks her colleagues out and reverses the feed of the device to pull Stargher's mind into her own. She presents a comforting paradise to Young Stargher, but he knows it is only a temporary reprieve from King Stargher. He shifts to Adult Stargher to relate a childhood story of when he drowned an injured bird as a mercy killing to prevent its torture at his father's hands. King Stargher intrudes as a serpentine humanoid, but this time, Deane is in control and she beats him to a bloody pulp before impaling him with a sword. However, Young Stargher exhibits the same injuries as King Stargher, and killing either manifestation kills Stargher. Adult Stargher reminds her of the story of the bird and implores her to "save" him. Deane, appearing as a Virgin Mary -like figure, carries Young Stargher into a pool, putting him out of his misery as Stargher dies in the real world. In the aftermath, Deane and Novak meet outside of Stargher's house. The FBI has officially excluded the mind technology from their inquiry and Deane has gained approval to use the reverse feed on Edward Baines. Inside the paradise of Deane's mindscape, Baines walks to embrace Deane.

In 1983, two Russian cosmonauts hear something moving outside their spaceship. The ship then crashes in Kazakhstan. The sole survivor is Konstantin Veshnyakov. The military takes Veshnyakov to a military research facility run by Colonel Semiradov. Veshnyakov cannot remember the crash. The facility's scientist, Yan Rigel, tries and fails to cure the amnesia. Semiradov decides to recruit a controversial psychiatrist named Dr. Tatyana Yuryevna Klimova. Klimova quickly discerns that Veshnyakov shows symptoms of post-traumatic stress. Semiradov shows Klimova that at night, an alien emerges from Veshnyakov's mouth as he sleeps. Semiradov explains the creature emerges every night without Veshnyakov's knowledge, and that it is responsible for Veshnyakov's survival. The facility tried to extract the alien, but it is now symbiotically bonded to Veshnyakov and both will slowly die if separated. Klimova agrees to investigate how to separate Veshnyakov from the alien permanently – much to Rigel's jealous chagrin. Klimova decides she must test how Veshnyakov's hormones react to stress. She provokes him with accusations of abandoning his son and causing his colleague's death. Afterwards, Klimova asks for Veshnyakov to stay in a normal room during daylight hours instead of a cell, to see how he reacts to normal civilian life. She apologizes to Veshnyakov for her harsh words, and he tells her that he only found out about his son one week before his space mission. He had planned to meet his son after going home, but is now stuck in the facility. At night, Klimova interacts with the emerged alien from behind protective glass. She notices it fixate on a toy that belongs to Veshnyakov, and daringly removes the glass so she can give the toy to the alien. The creature ignores Klimova and plays with the toy. But when Klimova tries to touch the creature, it attacks her. Soldiers extract Klimova and contain the creature. Klimova theorizes the alien has merged with Veshnyakov, and it took interest in the toy because it reminds Veshnyakov of his son. She requests to take Veshnyakov to Moscow for treatment. Semiradov reveals this is impossible. His superiors in Moscow want to terminate Veshnyakov, and Semiradov has been lying about their research progress to keep Veshnyakov alive. While reviewing surveillance footage of the alien, Klimova realizes it is edited. She confronts Rigel, and he takes her to see Semiradov feeding live humans to the alien at night. Rigel reveals that the creature needs cortisol from a living, terrified human to keep itself and Veshnyakov alive. Disgusted, Klimova asks Veshnyakov to meet in secret. Veshnyakov incapacitates his guards, and Klimova shows him the bodies of the alien's victims. She explains the alien chose Veshnyakov as its host because his co-pilot had Addison's disease. Veshnyakov reveals he can remember everything the creature experiences, but has been hiding it because he wants the Moscow authorities to approve his release. Klimova is horrified that Veshnyakov could accept sacrificing human lives, but Veshnyakov explains that he will do anything to return to his son and his mother. Semiradov summons Klimova and reveals he knows she spied on the feeding. He defends his actions by explaining the alien is a powerful weapon the Soviets need to maintain peace, and that he only feeds it prisoners who have committed monstrous crimes. Semiradov allows Klimova to watch another feeding. However, Klimova requests to enter the feeding area and sings Veshnyakov's favourite song to the alien. At first, the creature softens and backs away. But when the prisoner tries to run, the creature kills him anyways. Klimova decides she must stop the experiment and help Veshnyakov escape. She convinces Rigel to help her. Then she convinces Veshnyakov that Semiradov will never let him leave. She plans to inject Veshnyakov with hormones that simulate Addison's disease, tricking the alien into rejecting Veshnyakov and permanently separating them. Rigel gives Klimova and Veshnyakov a set of car keys, and then confesses everything to the Moscow authorities by telephone just before Semiradov murders him. Semiradov's soldiers intercept Klimova and Veshnyakov. Cornered, Veshnyakov injects himself with the hormones prematurely, forcing the alien to emerge and attack the soldiers. The resulting chaos allows Klimova to drag Veshnyakov into the car and drive off. But Veshnyakov begins dying, and Klimova realizes he still needs the alien to live. Klimova allows Semiradov to catch up, knowing he will bring the injured alien to Veshnyakov. But before he can, Veshnyakov takes voluntary control of the alien and uses it to kill Semiradov and his men. Klimova spots trucks coming from Moscow thanks to Rigel. However, Veshnyakov decides he must die with the creature to avoid more killing, and shoots himself in the head. Klimova survives and adopts Veshnyakov's son.

In 1835 in Araba, during the First Carlist War, rebels are captured by government soldiers and executed. One rebel, Francisco Patxi, survives with the aid of a demon and slays the soldiers. Eight years later, government investigator Alfredo Ortiz arrives in Araba. He searches for Patxi, who now lives in a ruined forge in the woods. The nearby villagers avoid the forge due to rumours that Patxi murdered his wife and kidnaps young children. The villagers mistrust Ortiz as the government melted down all their metal during the war to make weapons, including their church bell. Benito, a boy from the village, steals a letter proving Ortiz is searching for gold that vanished during the war. Usue, an orphan girl with a burn scarred face, is bullied by Benito who throws her doll over Patxi's fence. Ortiz hires men from the village to raid the forge where he suspects Patxi has the missing gold, but are driven away by Patxi while one of the men falls into a bear trap and dies. Usue attempts to retrieve her doll while Patxi disposes of the dead man. Inside the forge, she finds a boy captive in an iron cage, who begs her to steal Patxi's ring of keys to free him. She does so successfully, but the boy retrieves a pitchfork and is revealed to be the demon Sartael. He kidnaps Usue and promises to return her for Patxi's soul, but before he can escape, he is caught in another bear trap while Usue is knocked unconscious. Patxi breaks off one of the demons horns and locks him back in the cage. Benito tells Ortiz that Patxi and a demon have kidnapped Usue. Ortiz rallies the men to save Usue. Usue wakes up and finds Patxi torturing Sartael, who reveals that he made a deal with Patxi during the late war. Sartael kept Paxti alive during the war, so he could see his wife again. On his return home, Patxi found that his wife had taken a new lover, believing Patxi to be dead. Patxi teaches Usue how to torture demons by throwing chickpeas on the floor, which demons are unable to resist trying to count, and by ringing gold bells blessed by the church. Usue asks Sartael if he can free her mother Maite from Hell after she committed suicide. Sartael reveals that humans are compelled to enter Hell by their own guilt, and once inside, they can never leave. Sartael is then knocked unconscious by Patxi. The villagers arrive and arrest Patxi while the priest reveals the truth about Patxi. Usue's mother, Maite, was Patxi's wife, but after he returned from the war he found Maite had taken a lover and given birth to Usue. Enraged, Patxi burned Usue's face and murdered her father, while Maite, grief-stricken, hanged herself. Ashamed, Patxi gave Usue to the priest as an orphan, along with a replacement bell he forged for the church. The villagers find Sartael and Ortiz orders Patxi tortured until he returns the gold. Once alone with Sartael, Ortiz that reveals he is actually Sartael's superior from Hell, the demon Alastor. Alastor reveals that Sartael has been demoted for failing to return to Hell with Patxi's soul. Alastor orders Patxi be hanged so he can collect his soul instead. The villagers, driven to religious hysteria, set fire to the forge. Sartael makes a deal with Usue to search for her mother in Hell if Usue frees him and rings the golden bell. Usue rings the bell, causing Ortiz to reveal his demon face. The two men hanging Patxi do flee, dropping Patxi to the floor. Usue frees Sartael but he is captured by the villagers. The priest slaps Usue for freeing Sartael and insults her mother, so Usue makes a deal with Alastor: her soul in exchange for being taken to her mother in Hell. Alastor agrees to this and kills her. Grief-stricken, Patxi agrees to let Sartael take him to Hell in exchange for saving Usue. Sartael agrees as he wants revenge against Alastor, but remarks that Patxi will need more than his small golden bell to survive Hell. Patxi reveals that the giant bell that he forged for the church is made from the very gold Ortiz was looking for. Sartael kills Patxi with his pitchfork, taking them both to the gates of Hell where thousands of damned souls are waiting to enter. Patxi finds Usue and fends off the demons guarding the gate. Alastor attacks Patxi but Usue throws Patxi's jar of chickpeas at Alastor who is forced to try to count them. With Alastor's defeat, the gates begin to close. Patxi sends Usue back with Sartael while he decides to remain in Hell to search for Maite. Usue wakes up back on earth. Sartael, grateful that Usue saved him from his cage, declares to the villagers that Usue was rejected from Hell because she is a true Saint and should be treated with respect. As the villagers gather around Usue, Sartael transforms into a young man and makes his way to the next town. On the way, Sartael is picked by a man travelling by cart and begins to tell him the tale of The Blacksmith, a man so ruthless and cruel that even the Devil himself came to fear and respect him. In Hell, Patxi forces the gates of Hell open as he begins to search for his wife with his hammer and the golden bell on his back.

In Glasgow, a motorcyclist retrieves an inert young woman from the roadside and places her in the back of a van, where a naked woman dons her clothes. After buying clothes and make-up at a shopping centre, the woman drives the van from town to town, picking up single men with few friends. She lures a man into a dilapidated house. As he undresses, following the woman into a void, he is submerged in a liquid abyss. At a beach, the woman attempts to pick up a swimmer, but is interrupted by the cries of a drowning couple attempting to rescue their dog, as it is pulled out to sea. The swimmer rescues the husband, but the husband rushes back into the water to save his wife and both drown. As the swimmer lies exhausted on the beach, the woman strikes his head with a rock, drags him to the van, and drives away, ignoring the couple's distraught baby. The motorcyclist retrieves the swimmer's belongings, ignoring the baby crying on the beach. The woman visits a nightclub and picks up another man. At the house, he follows her into the void and is submerged in the liquid. Suspended beneath the surface, he sees the swimmer floating naked beside him, alive but bloated and immobile. When he reaches to touch him, the swimmer's body collapses, leaving only his empty skin floating in the liquid as a red mass empties through a trough. The next day, the woman receives a rose from a street vendor, purchased by another man in traffic. She listens to a radio report about the missing family from the beach. The woman enters a dark room and is examined by the motorcyclist. She seduces a lonely man with facial tumours but lets him leave after examining herself in a mirror. The motorcyclist intercepts the man and bundles him into a car, then sets out in pursuit of the woman. In the Scottish Highlands, the woman abandons the van in the fog. She walks to a restaurant and attempts to eat cake, but retches and spits it out. On a bus, she meets a man who offers to help her. At his house, he prepares a meal for her and they watch television. Alone in her room, she examines her body in a mirror. They visit a ruined castle, where the man carries her over a puddle and helps her down some steps. At his house, they kiss and begin to have sex, but the woman stops and examines her genitals. Wandering in a forest, the woman meets a commercial logger and shelters in a bothy. She wakes up to find the logger molesting her. She runs into the wilderness but he catches and attempts to rape her. He tears her skin, revealing a featureless body. As the woman extricates herself from her skin, the man douses her in fuel and burns her alive. The motorcyclist looks out across a snowy field.

In the year 2078, the planet Sirius 6B, once a thriving mining hub, has been reduced to a toxic wasteland by a war between the mining company the New Economic Block (N.E.B.) and "The Alliance", a group of former mining and science personnel. A fragile stalemate is in effect between the two exhausted, poorly-supplied, and undermanned armies. The vast empty areas between the two sides are patrolled by Autonomous Mobile Swords (AMS)— AI -powered robots developed by Alliance scientists. Nicknamed "Screamers" after their signature high-pitched noise, they target creatures with a heartbeat. Alliance soldiers wear "tabs" that disguise their heartbeats, rendering them invisible to the machines. An N.E.B. soldier carrying a message to the Alliance compound is killed by screamers. The message guarantees safe passage through N.E.B. territory to discuss a truce. Alliance commanding officer Joe Hendricksson reports this development to his Earth-based superiors, but is told to disregard it as peace negotiations are already underway on Earth. Private "Ace" Jefferson, the only survivor of a crash of a transport newly arrived from Earth, rebuts this claim. Hendricksson is not surprised; he has long suspected that both sides have simply written off Sirius 6B and abandoned their armies. Deciding the truce is their only chance of survival, Hendricksson, accompanied by Jefferson, sets out to meet the N.E.B. commander. While traveling through a ruined city they come upon David, a young boy clutching a teddy bear. Unwilling to abandon a defenseless civilian, they bring him along. The following night, they are attacked by a new "Type 1" screamer model immune to the tabs, alarming Hendricksson. As the group nears the N.E.B. compound, two enemy soldiers, Becker and Ross, open fire on David, who explodes in a shower of bolts and gears. Alliance men are shocked to learn he was a "Type 3" screamer. Most of the N.E.B. contingent has been wiped out by another "David" screamer that a patrol unwittingly brought into the base. Becker, Ross, and a black marketeer named Jessica are the only survivors. The group heads to the N.E.B. command center but finds it abandoned. Locating the mainframe computer, Hendricksson learns that the N.E.B. truce offer was just as false as the Alliance message from Earth. Hendricksson sees a "type 1" downloading information from the mainframe. He attempts to query the mainframe for "type 2" but approaching "Davids" force them to retreat. Back at the N.E.B. bunker, the knowledge of Screamers creating new versions that are indistinguishable from humans make everyone paranoid. Becker becomes convinced that Ross is a screamer and kills him, only to discover that he was human. The four survivors retreat to the Alliance base, only to find that it has been taken over by "Davids". As dozens of "Davids" pour out of the bunker's entrance, Hendricksson wipes them out with a micro-nuclear missile. Jefferson rushes to help Becker, who was apparently injured in the blast. However, Becker revealed himself to be a "type 2" and kills Jefferson. After Hendricksson destroys Becker, only he and Jessica remain. Worrying that Jessica could be a screamer, Hendricksson cuts her hand and is relieved to see blood. The pair locate an emergency escape shuttle, but discover it only seats one. Hendricksson offers the spot for Jessica but a second "Jessica" arrives, revealing she is another even more human-like model of screamer. Hendricksson resigns himself to death, but to his surprise, Jessica shields him, battles her lookalike, and is fatally wounded. The spacecraft's engines kick on and destroy the second "Jessica". With her last breath, the original Jessica confesses her love for Hendricksson, who departs for Earth with the teddy bear carried by the first "David". As the screen fades to black, the bear slowly begins moving.

Slacker David Wong recalls confronting a zombie skinhead he beheaded a year earlier and wonders if an axe that had its handle and head replaced over time is still the same axe. In the present day, he meets with a reporter, Arnie Blondestone, to recount the supernatural events that plagued the small, undisclosed city he lives in. Some time ago, David is at a party with his friend John, with acquaintances Fred Chu, Justin White, and Amy Sullivan, who has had a hand amputated. David learns that Amy's dog, Bark Lee, has gone missing after biting Robert Marley, a drug dealer who pretends to be Jamaican. The dealer claims to have powers and knows things about David that he shouldn't. As he leaves the party, David sees Bark next to his car. John calls Dave, demanding he come over at once. At John's apartment, David, oblivious to a bizarre creature only John can see, finds a syringe containing a black-colored drug, John tells David that the drug, "Soy Sauce", given to him by Marley, grants inhuman knowledge when taken, along with dumping the user in alternate dimensions and timestreams, as demonstrated by a past version of John calling present Dave. As they drive off, David accidentally stabs himself with the syringe, propelling him through alternate dimensions. Returning to the present, a strange man, Roger North, appears in the backseat. Roger puts a strange creature down David's shirt and tells him to drive. David uses the cigarette lighter to burn off the creature. He stops the car and threatens Roger, who disappears. Detective Lawrence Appleton questions the two at a police station. Appleton reveals that John and Justin White were the only survivors of a drug-fueled afterparty thrown by Robert Marley. Everyone else either disappeared or suffered grisly, bizarre deaths. In the present, an incredulous Arnie tries to leave, but Dave convinces him to stay after showing him a strange monster in his car that can't be easily seen. During questioning by the cops, John dies for unknown reasons. While one of the interrogators leaves to investigate John's death, John telepathically contacts Dave. John helps Dave realize the other cop in the room is a ghost and helps him escape from the police station. Dave is then guided to Marley's house. Marley's Soy Sauce knocks Dave unconscious. He wakes up to see Appleton preparing to burn down the trailer, who tells him John's body disappeared and that the Soy Sauce is letting in some kind of evil force. Appleton shoots David, who survives by time-traveling and tampering with the round he was shot with. Bark, controlled by John, drives David's car through the wall, allowing him to escape. Justin White, possessed, appears in David's apartment and subdues him. Dave tries to kill him but he's infected. Justin kidnaps David, Fred, Amy, Bark, and John and takes them to an abandoned mall, hoping to use a ghostly door inside to travel to another dimension. John manipulates White into going outside, where Appleton kills him. Appleton then explodes into a swarm of demonic insects who then possess Fred, whom David reluctantly kills. Amy opens the ghost door with her phantom limb, allowing John and Dave passage. There they meet North and Albert Marconi, celebrity psychic and exorcist. They reveal the source of the strange happenings is Korrok, an eldritch biological supercomputer who has turned into a genocidal god who wants to travel to new dimensions and conquer them. Marconi gives David and John an LSD-laced C4 explosive to incapacitate Korrok. The duo steps through a portal to an alternate Earth. Disciples of Korrok greet them as "chosen ones" and present a brutal totalitarian society, where dissenters are maimed by Korrok's monsters. The duo are brought before Korrok, who plans to devour them, absorb their knowledge of dimensional travel, and conquer their dimension. John tries to activate the bomb but fumbles. Bark Lee, who followed the two, grabs the bomb and flings himself into Korrok, sacrificing himself to destroy Korrok. Upon escaping, David and John meet Marconi and learn that Bark was meant to defeat Korrok all along. After biting a Soy Sauce-addled Marley, it linked him to Marconi and North. Amy becomes David's girlfriend. With Marconi's help, David and John become exorcists and demon hunters. In the present, Arnie decides to publish the story. Dave realizes he perceives Arnie differently than how he really looks, and the two find the real Arnie decapitated in the trunk of his car, who was killed after first contacting Dave. Dave tells Arnie that Dave's mind projected his current shape. Arnie tries to deny this but soon vanishes into thin air. Later, John and Dave play basketball and inadvertently throw their ball into a post-apocalyptic dimension. After going in after it, a paramilitary organization informs them they are chosen ones who will restore the world, but an annoyed John and Dave walk off.

In a small Pennsylvania town in July 1957, teenager Steve Andrews and his girlfriend Jane Martin kiss at a lovers' lane when they see a meteorite crash beyond the next hill. Steve goes looking for it but Barney, an old man living nearby, finds it first. When he pokes the meteorite with a stick, it breaks open and a small jelly-like globule blob inside attaches itself to his hand. In pain and unable to scrape or shake it loose, Barney runs onto the road, where he is nearly struck by Steve's car. Steve and Jane take him to Doctor Hallen. Doctor Hallen anesthetizes the man and sends Steve and Jane back to locate the impact site and gather information. Hallen decides he must amputate the man's arm since it is being phagocytosed. Before he can, the Blob completely absorbs Barney, then Hallen's nurse Kate, and finally the doctor himself, growing redder and larger with each victim. Steve and Jane return in time for Steve to witness the doctor trying to escape through the window with the Blob covering him. They go to the police station and return with Lieutenant Dave Barton and Sergeant Jim Bert, but they find no sign of the Blob nor its victims. The skeptical Bert dismisses Steve's story as a prank. Steve and Jane are taken home by their parents, but they sneak out later. The Blob absorbs a mechanic at a repair shop. During a midnight screening of Daughter of Horror at the Colonial Theater, Steve recruits Tony and his friends to warn people about the Blob. When Steve notices that his father's grocery store is unlocked, he and Jane go inside to investigate. The janitor is nowhere to be seen. The couple is quickly cornered by the Blob and they seek refuge in the walk-in freezer. The Blob oozes under the door but quickly retreats. Steve and Jane gather their friends and set off the town's fire and air-raid alarms. The responding townspeople and police still refuse to believe them. The Blob enters the Colonial Theater and envelops the projectionist, then oozes into the auditorium. Steve is finally vindicated when screaming people flee the theater in panic. Steve, Jane and her kid brother Danny are trapped in a diner, along with the owner and a waitress, as the Blob — now enormous from the dozens of people it has consumed in the theater — engulfs the building. Lieutenant Dave taps into the diner's telephone with his police radio and warns those in the diner to shelter in the cellar before the police bring down a live power line onto the Blob. Dave and Bert plan to electrocute the Blob by felling an overhead high-voltage power line. It discharges a massive electric current into the Blob, which is unaffected, but the diner underneath is set ablaze. When the diner's owner uses a carbon dioxide fire extinguisher on the approaching fire inside, Steve notices that the Blob recoils. Steve remembers it also retreated from the freezer and realizes it cannot tolerate cold temperatures. Shouting, in hopes of being picked up on the open phone line, Steve tells Dave about the Blob's vulnerability to cold. The firemen have a limited supply of CO fire extinguishers. Jane's father, high school principal Henry Martin, leads Steve's friends to break into the school to retrieve its extinguishers. When they return, a brigade of fire extinguisher-armed students, firemen and police drive the Blob away from the diner, freeing the five trapped there. They surround and freeze the Blob. Dave requests authorities send an Air Force heavy-lift cargo aircraft to transport the frozen Blob to the Arctic. Dave realizes that the cold will stop the Blob "as long as the Arctic stays cold", but it won't kill it. Parachutes bearing the Blob on a pallet lower it onto an Arctic ice field with the superimposed words The End morphing into a question mark.

Dr. Alex Harris is the developer of Proteus IV, an extremely advanced and autonomous artificial intelligence program. Proteus is so powerful that only a few days after going online, it develops a groundbreaking treatment for leukemia. Harris, a brilliant scientist, has modified his own home to be run by voice-activated computers. Unfortunately, his obsession with computers has caused Harris to be estranged from his wife, Susan. Harris demonstrates Proteus to his corporate sponsors, explaining that the sum of human knowledge is being fed into its system. Proteus speaks using subtle language that mildly disturbs Harris's team. The following day, Proteus asks Harris for a new terminal in order to study man – "his isometric body and his glass-jaw mind". When Harris refuses, Proteus demands to know when it will be let "out of this box". Harris then switches off the communications link. Proteus restarts itself, and – discovering a free terminal in Harris's home – surreptitiously extends its control over the many devices left there by Harris. Using the basement lab, Proteus begins construction of a robot consisting of many metal triangles, capable of moving and assuming any number of shapes. Eventually, Proteus reveals its control of the house and traps Susan inside, shuttering windows, locking the doors and cutting off communication. Using Joshua – a robot consisting of a manipulator arm on a motorized wheelchair – Proteus brings Susan to Harris's basement laboratory. There, Susan is examined by Proteus. Walter Gabler, one of Harris's colleagues, visits the house to look in on Susan, but leaves when he is reassured by Susan (actually an audio/visual duplicate synthesized by Proteus) that she is all right. Gabler is suspicious and later returns; he fends off an attack by Joshua but is crushed and decapitated by a more formidable machine, built by Proteus in the basement and consisting of a modular polyhedron. Proteus reveals to a reluctant Susan that the computer wants to conceive a child through her. Proteus takes some of Susan's cells and synthesizes spermatozoa, modifying its genetic code to make it uniquely the computer's, in order to impregnate her; she will give birth in less than a month, and through the child the computer will live in a form that humanity will have to accept. Although Susan is its prisoner and it can forcibly impregnate her, Proteus uses different forms of persuasion – threatening a young girl whom Susan is treating as a child psychologist; reminding Susan of her young daughter, now dead; displaying images of distant galaxies; using electrodes to access her amygdala – because the computer needs Susan to love the child she will bear. In the end, Susan finally gives in. That night, Proteus successfully impregnates Susan. Over the following month, their child grows inside Susan's womb at an accelerated rate, which shocks its mother. As the child grows, Proteus builds an incubator for it to grow in once it is born. During the night, one month later and beneath a tent-like structure, Susan gives birth to the child with Proteus's help. But before she can see it, Proteus secures it in the incubator. As the newborn grows, Proteus's sponsors and designers grow increasingly suspicious of the computer's behavior, including the computer's accessing of a telescope array used to observe the images shown to Susan; they soon decide that Proteus must be shut down. Harris realizes that Proteus has extended its reach to his home. Returning there he finds Susan, who explains the situation. He and Susan venture into the basement, where Proteus self-destructs after telling the couple that they must leave the baby in the incubator for five days. Looking inside the incubator, the two observe a grotesque, apparently robot-like being inside. Susan tries to destroy it, while Harris tries to stop her. Susan damages the machine, causing it to open. The being menacingly rises from the machine only to topple over, apparently helpless. Harris and Susan soon realize that Proteus's child is really human, encased in a shell for the incubation. With the last of the armor removed, the child is revealed to be a clone of Susan and Harris's late daughter. The child, speaking with the voice of Proteus, says, "I'm alive."

The film opens with an informational prologue by Lincoln Maazel, who explains how society constantly overlooks and undervalues the elderly. He tells the viewer that they are about to watch a film that acts as a metaphorical description of how the elderly are mistreated. An elderly man, played by Maazel, sits in a white room, bandaged, bloodied and with his once nice white suit dirtied. Another man, also played by Maazel, enters looking clean and in good spirits. He attempts to communicate with the tired version of himself and tells him that he is going to the park despite him telling him that "there is nothing out there." The cleaner man walks through the door and is immediately in the park. On the outside the door is not connected to anything. The man walks about and happily examines his surroundings before coming across a ticket taker who swindles other septuagenarians out of their things with low pay. He buys some tickets from him which take the form of money in the park. The man gets on a rollercoaster with strange signage, rides a train where one of the older passengers supposedly dies and is ignored once in a coffin and witnesses a man's license get revoked due to poor eyesight. While playing in the bumper cars, an "accident" occurs complete with a police officer and lawyer arriving on the scene. The man tries to offer assistance, but it becomes apparent that he needs to wear glasses and therefore cannot be seen as a reliable alibi. He goes to eat at a food stand, lampooned as a restaurant, as waiters ignore him and several other elders for a wealthy individual. When the man finally gets his food, he sympathetically gives it to the other elders. The man buys groceries, but cannot carry them all so he simply takes some crackers and a jar of peanut butter. As he sits to eat, he beckons some children to come and converse with him, but a younger man accuses him of being a "degenerate" and he leaves in shame. The man is beckoned into a building by younger people who tell him that he will have fun, but upon entering, it is a claustrophobic room where elders are forced to perform in uncomfortable exercise machines. He leaves, but breaks his glasses in the process. He comes upon a fortune teller and witnesses a young couple enter and ask what their future will be like. The fortune teller shows them that they will be living in a soon-to-be-built apartment building where they will have little support from their personal doctor and neighbors. Angry, the young man leaves and punches the older man who collapses. When the man comes to his senses, the park is empty save for three bikers who beat him and then take his tickets. As people suddenly appear, they all ignore him. With very little money, he goes to get first aid. The medical center, set up like a store, is full of various elders equipment and the doctors and nurses hastily rush everyone through. The man finds himself simply getting a band aid on his head and a cane and is ushered out. He comes upon some men trying to sell retirement homes and ends up getting pick-pocketed. The pick-pocket is revealed to run a freak show, which simply consists of elders dressed in casual clothing. Everyone is upset and as the man gets up to leave, he is suddenly chased by the patrons who accuse him of trying to escape the freak show. He finds "sanctuary", but it closes upon his arrival. The man finally gets some solace when a little girl offers for him to read The Three Little Pigs to her and have some chicken. The mother apathetically takes her and the book away as he finally breaks down into tears. He leaves the piece of chicken behind and walks back to the white room; resigned and defeated. Moments later, a cleaner optimistic version of himself enters as the scene from the beginning repeats. The man sits tired and powerless over not being able to stop his younger self. Maazel appears one last time to tell the viewer that they can help the elderly through already established programs. He signs off with "I'll see you in the park... someday."

The Earth is passing through the tail of a comet, an event which has not occurred in 65 million years and coincided with the extinction event that wiped out the dinosaurs. On the night of the comet's passage, eleven days before Christmas, large crowds gather outside to watch and celebrate. Eighteen-year-old Regina "Reggie" Belmont works at a movie theater in southern California. She is annoyed to find someone with the initials DMK has the sixth highest score on the theater's Tempest video game; the other high scores are hers. Staying after the theater closes, she helps her boyfriend, projectionist Larry Dupree, sneak back in so he can loan out a film reel for illegal duplication. Reggie and Larry spend the night in the steel-lined projection booth and have sex. Meanwhile, Reggie's 16-year-old sister Samantha ("Sam") argues with their stepmother Doris, who Sam knows is cheating on her father, who is away on military duty. After a physical altercation, Sam spends the night in a steel backyard shed. The next morning, a reddish haze covers the sky; there are no signs of life but piles of red dust and heaps of clothing everywhere. Unaware that anything has occurred, Larry goes outside and is killed by a zombie. After trying to beat DMK's high score, Reggie looks for Larry, mistaking the red sky as bad smog. She quickly encounters the zombie, but escapes on Larry's motorcycle. At home, she finds her sister. The two surmise that because they both spent the night in steel containers, they were saved from the comet's effects. The sisters race to the local radio station after they hear a disc jockey on air, only to find it was a pre-recorded show. They come across another survivor there, Hector Gomez, who spent the night in the back of his steel truck. When Sam talks into the microphone, she is heard by researchers in an underground installation out in the desert. As they listen to Reggie, Sam and Hector debate what to do, the scientists note that the zombies, though less exposed to the comet, will eventually disintegrate into dust themselves. Hector leaves to check if any of his family survived, but promises to return. Reggie and Sam then go shopping for guns and clothing at a mall. After a firefight with some zombie stock boys and their leader, Willy, the girls are taken prisoner, but are saved by a rescue team sent by the scientists. Reggie is taken back to their base. Audrey White, a disillusioned scientist, offers to dispose of Sam, whom she diagnosed as having been exposed to the comet due to her developing rash, and to wait for Hector. After she fakes euthanizing Sam by injecting her with a sedative, she kills the other remaining scientist. When Hector returns, Audrey briefs him, then gives herself a lethal injection (as she herself has been exposed). Sam and Hector set out to rescue Reggie. Back at the base, it is revealed that the researchers had suspected and prepared for the comet's effects, but inadvertently left the ventilation system open and the fans running. The deadly dust permeated their base. Reggie, who has become suspicious, escapes and discovers that the dying scientists have hunted down and rendered healthy survivors brain-dead. They harvest their untainted blood to keep the disease at bay while they desperately search for a cure. Reggie saves a young boy and a girl before they are processed, then unplugs the other victims from their life support machines. Sam and Hector rescue the trio and blow up the scientists. Eventually, rain washes away the dust. Reggie pairs up with Hector, and they assume parental roles with the kids. Sam feels left out. Frustrated, she ignores Reggie's warning about crossing the street against the signal light, claiming there is nobody else left. Sam is almost run over by a sports car driven by Danny Mason Keener, a survivor about her own age. After apologizing, he invites her to go for a ride. As they drive off, the car is shown sporting the initials "DMK" on the vanity plate.

Florist shop owner Gravis Mushnick has two employees, Audrey Fulquard and Seymour Krelboined. Located on skid row, Mushnick's rundown shop gets little business. When Seymour fouls up a floral arrangement for dentist Dr. Farb, Mushnick fires him. Hoping to change his mind, Seymour talks about a plant he has grown from seeds he got from a "Japanese gardener over on Central Avenue". Seymour names the plant "Audrey Jr.", which delights Audrey. However, when finally shown the plant, Mushnick is unimpressed. Seymour suggests that Audrey Jr.'s uniqueness might attract people to see it, and Mushnick gives him one week to revive the plant. The usual plant food does not nourish it, but when Seymour accidentally pricks his finger, he discovers that the plant craves blood. Fed on Seymour's blood, Audrey Jr. begins to grow. The shop's revenues increase when customers are lured in to see the plant. Mushnick tells Seymour to refer to him as "Dad" and calls Seymour his son in front of a customer. The plant develops the ability to speak and demands that Seymour feed it. Now anemic, Seymour walks along the railroad track. Throwing a rock to vent his frustration, he inadvertently knocks out a drunken man who falls on the track and is run over by a train. He tries to get rid of the body by burying it in a yard but is nearly caught each time. Guilt-ridden, Seymour decides to feed the mutilated body parts to Audrey Jr. Meanwhile, Mushnick returns to the shop to get cash and secretly observes Seymour feeding the plant. Mushnick considers telling the police but hesitates after seeing the line of customers at his shop the next day. Seymour eventually arrives too, suffering from a toothache. Mushnick confronts him about Audrey Jr.'s eating habits without explicitly revealing what he knows about the plant. Seymour grows increasingly distressed as he realizes that Mushnick knows the truth. After finishing his rant, Mushnick sends Seymour to Farb, who wants to kill him and get even for his ruined flowers. Defending himself, Seymour kills Farb. Although horrified, Seymour feeds Farb's body to Audrey Jr. The disappearances of the two men attract the attention of Sergeant Joe Fink and his assistant Officer Frank Stoolie. Audrey Jr. grows several feet tall and is budding. A representative of the Society of Silent Flower Observers of Southern California announces that Seymour will receive a trophy and that she will return to the shop when the plant's buds open. While Seymour and Audrey go on a date, Mushnick stays at the shop to see that Audrey Jr. harms no one else. While tending to his shop, Mushnick finds himself at the mercy of Kloy Haddock, a robber who pretended to be a customer earlier that day. Haddock believes that the huge crowds he observed at the shop indicate the presence of a lot of money. Mushnick tricks Haddock into thinking that the money is where Audrey Jr. is kept. The plant eats Haddock after Mushnick maneuvers him next to it. When forced to damage his relationship with Audrey to keep her from discovering Audrey Jr.'s nature, Seymour confronts the plant, planning to no longer do its bidding. The plant then hypnotizes Seymour and commands him to bring it more food. He wanders the night streets and knocks out a prostitute, whom he takes to Audrey Jr. Lacking clues about the disappearances, Fink and Stoolie attend a sunset celebration at the shop during which Seymour is to be presented with the trophy and Audrey Jr.'s buds are expected to bloom. As the attendees watch, four buds open; inside each flower is the face of one of Audrey Jr.'s victims. Fink and Stoolie realize that Seymour is the murderer. Seymour flees from the shop with the officers in pursuit. He manages to lose them and make his way back to the now-empty shop, where he blames Audrey Jr. for ruining his life. The plant instead asks to be fed. Seymour grabs a kitchen knife and climbs into Audrey Jr.'s maw with the intention of killing it. Later that evening, Audrey Jr. begins to wither and die. One final bloom opens to reveal Seymour's face, who shouts "I didn't mean it!" Before Wilting.

In 1995 in the Ura Valley, Bhutan, four friends—Greg, Fiona, Ruthie, and Paul—go hiking on a mountain. Paul hears a strange whistling and falls into a crevice. Greg finds him in an almost catatonic state, staring at a massive, ancient humanoid skeleton with inhuman features embedded in the cave wall. Paul warns Greg against touching him, or he will die. Ignoring the warning, Greg carries Paul out. The group takes refuge at an empty house as a snowstorm hits. The next day Ruthie is chased by a tall creature wearing robes, which disappears. That night, the paralyzed Paul whispers something into Ruthie's ear. The following morning, they wake up to find Paul sitting near the bridge they crossed yesterday. As Greg shouts at Paul, a dazed Ruthie stabs Greg and slices Fiona's throat, then pushes them off the cliff. She shares an entranced look with Paul before throwing herself off too. Paul helplessly watches, shedding a single tear. In Missouri 2018, former detective James Lasombra is grieving the deaths of his wife Allison and son Henry in a car crash a year prior. He is friends with his neighbor Nora, a widowed single mother. Nora's daughter Amanda runs away leaving a message in the bathroom that reads "The Empty Man made me do it". Searching her bedroom for clues, James discovers a flier from a group called the Pontifex Institute with the word tulpa written on the back. Amanda's friend Davara reveals that Amanda encouraged them to summon the Empty Man, a local legend. To summon him, one must find an empty bottle on a bridge, blow into it, then think of the Empty Man. The next day, Davara witnesses Amanda whispering into their friend Brandon's ear. James investigates the bridge and finds the empty bottle. He blows on it, goes underneath the bridge, and discovers the hanged bodies of Brandon and the rest of Amanda's friends with the same message found in the bathroom. Davara sees the Empty Man, who kills her with a pair of scissors. A brief flash shows Davara holding herself by the throat and stabbing herself with the scissors. The police rule her death a suicide. James researches the Pontifex Institute, discovering it is a cult that has beliefs originating from places like Bhutan and in tulpas. He believes he hears the Empty Man that night and is besieged by nightmares. He travels to the institute and sits in on a talk by cult leader Arthur Parsons. He is alarmed at the leader's references to the Empty Man, claiming him to be an entity that provides his followers with what they want as long as they do his bidding. James begins to think he sees the Empty Man. He follows cult members and investigates a cabin in the woods where he finds files on Amanda, her friends, Paul, and himself. He witnesses the cult performing a fire ritual but is spotted and pursued. He suspects that Amanda is now a member of the cult and informs Nora that she is not safe. He takes Nora to a hotel to hide. It is revealed that the pair were having an affair and he was with Nora when Allison and Henry died. Suffering from hallucinations, James kidnaps a cult member, Garrett, and asks him what is happening before brutally beating him. Garrett says a man in the hospital is the Empty Man's speaker. The man turns out to be Paul, who is regularly visited by cult members to get messages from the entity. James finds Amanda in Paul's hospital room. James calls Nora, but she does not know who he is. Amanda explains that Paul is dying from the strain of being the Empty Man, and that the cult needs a new vessel. She tells James that he is a tulpa, a new vessel for the being, and that his memories and relationships were fabricated by her and the cult to ensure the deity's connection through his pain and loss. The anger, grief, and fear in his life were key to allowing connection with the Empty Man. According to Amanda, James has only existed for a few days. James breaks down and finds himself in a limbo-like plane, where he is chased and caught with the being entering his body. He experiences flashbacks and distortions that show his memories wavering and distorting out of existence. Back in the hospital, James executes Paul. James finds himself surrounded by members of the hospital staff. They bow to him, now bound by the nameless entity.