Struggling inventor Randall Peltzer visits a Chinatown antique store to find a Christmas present for his son, Billy. In it, Randall uncovers a small and furry creature called a mogwai (Cantonese: 魔怪, 'devil'). The owner, Mr. Wing, refuses to sell it to him, but his grandson secretly does, warning Randall to remember three important rules concerning its care – keep the creature away from light, especially sunlight, which will kill it; do not let it come in contact with water; and above all, never let it eat after midnight. In Randall's hometown of Kingston Falls, Billy works at its local bank, but fears that his dog Barney will be put down by widowed miser Ruby Deagle. His father returns and offers him the mogwai, now named "Gizmo", as a pet and informs him of the rules. Gizmo is friendly and docile, but when Billy's friend, Pete Fountaine, accidentally spills water on him, five more mogwai spawn from him – a more mischievous sort led by the aggressive Stripe, named after the mohawk -like tuft of white fur on his head. Billy shows one of the mogwai to his former elementary school science teacher, Roy Hanson, spawning another mogwai, whom the latter experiments on. Back home, Stripe and his fellow mogwai trick Billy into feeding them after midnight by sabotaging his bedside clock. They form cocoons, as does Hanson's mogwai, which soon hatch, emerging as destructive and reptilian imp-like monsters called "gremlins". Hanson is murdered by his gremlin, while those at the Peltzer house torture Gizmo and assault Billy's mother, Lynn. The duo are able to dispatch all the gremlins sans Stripe, who escapes to the local YMCA where he jumps into its swimming pool, spawning an army of gremlins that wreak havoc on Kingston Falls. Many locals are injured or outright killed during their rampage, including Deagle. The police are helpless in the ordeal, as they too fall victim to the gremlins' mischief. After Billy rescues his co-worker and girlfriend, Kate Beringer, when the gremlins attack the bar she works at, and they seek refuge in the bank, the latter discloses that her father went missing on Christmas Eve when she was nine years old, but was then found dead in their house's chimney several days later. Planning to surprise his family while portraying Santa Claus, he inadvertently slipped and broke his neck while climbing down the chimney. Still suffering from post-traumatic stress disorder due to the incident, Kate confesses how this led to her dislike of the holidays. The trio find the gremlins gathered in the local movie theater due to morning approaching and set off a natural gas explosion, killing them all except for Stripe, who left the theater earlier to retrieve candy at a Montgomery Ward store across the street. They follow Stripe into the store, where he attempts to use a fountain to spawn more gremlins, but Gizmo then opens a nearby skylight, exposing Stripe to sunlight and killing him. In the aftermath, Mr. Wing arrives at the Peltzer house to reclaim Gizmo as he scolds the family for their negligence and criticizes Western society for its carelessness with nature. However, as he turns to leave, Gizmo, having bonded with Billy, bids him goodbye. A compassionate Wing then concedes that Billy may be ready to properly care for him one day.

Rochel, an Orthodox Jew, and Nasira, a Muslim originally from Syria, are young women who are just beginning as teachers in New York's public school system. As Rochel is a teacher for the visually impaired, she meets Nasira, who teaches the fourth grade, as the aid for Eddie, one of Nasira's students. They bond while working together on Eddie's assignments, realizing that they share a lot in common. They also both fight against the stereotypes directed towards them, particularly from Principal Jacoby and Rochel's family. Both Nasira and Rochel are going through the process of an arranged marriage. Nasira is initially introduced to an older man, a friend of her father’s, whom she rejects. Her parents then introduce her to a young man her own age whom she likes. The system is different for Rochel, however, who is introduced to young men through the local Shadchan. While Nasira's parents ultimately listened to her frustrations and interests, Rochel's Shadchan only introduces Rochel to young men who fit the Shadchan's set of expectations, while ignoring what Rochel wants. After a few disastrous introductions, Rochel announces that she is stopping the process. She then temporarily leaves home to discuss the matter with her cousin, who has left the Orthodox tradition. Ultimately, through an accidental meeting with friends of her brother, including an Orthodox Jewish young man, it is Nasira who helps Rochel find someone she likes. The film ends with Nasira and Rochel both married, sitting in the park with their babies in their strollers, talking about their husbands and married life.

In 1992 Russia, music teacher Nikolay Chizhov moves into a communal apartment in St. Petersburg, where he discovers a mysteriously boarded-up window in his new room. During a housewarming party, he and his guests drunkenly descend from this window, believing it leads to the streets of St. Petersburg. Instead, they stumble upon a bar in Paris. The next day, Chizhov learns from a returning elderly resident that the window periodically opens to Paris for a few weeks every few decades. Realizing the limited time to access Paris, Chizhov's neighbor, Gorokhov, and his family begin cross-border ventures through the window, from selling souvenirs to transporting a Citroën 2CV into Russia. Alongside the whimsical exploits, Chizhov faces challenges in his career and personal life. After protesting the dismissal of music education at his school, he is fired, prompting a student strike in his support. He tries to find work in Paris, only to turn down an unusual gig at a nudist club. A romance develops between Chizhov and Parisian Nicole, whose apartment connects to the same rooftop as the magical window. When Gorokhov lures Nicole into Russia, she becomes lost and overwhelmed by the harsh realities of 1990s Russia before Chizhov ultimately helps her return to Paris. Later, fulfilling a promise to his students, Chizhov uses the window to show them Paris, but they miss the window's closing, forcing them to attempt a daring return to Russia by hijacking a plane. Months later, Chizhov and Gorokhov spot the old resident's cat emerging from a crack in the wall, sparking their hopes of reopening the path to Paris.

In Mile End, Montreal, Léo Lauzon is a young boy living in a tenement with his dysfunctional family, serving as the unreliable narrator. He uses his active fantasy life and the book L'avalée des avalés by Québécois novelist Réjean Ducharme to escape the reality of his life. He feels his father is insane and denies being his son. After having a dream revealing his mother was impregnated after falling into a cart of tomatoes contaminated by an Italian man's semen, Léo identifies as Italian rather than French Canadian and adopts the name Léolo Lozone. Growing up in an apartment with a rat in the bathtub, a turkey and a family obsessed with regular bowel movements, Léolo continues to write. His writings are discovered by the Word Tamer, a reincarnation of Don Quixote, who searches through trash for letters and photographs. Léolo observes a neighbouring young woman named Bianca and imagines her singing to him from a closet, emitting a white light. His grandfather, who Léolo believes attempted to murder him by holding him under a pool, helps her financially and extorts her for sexual favours, revealing her breasts and putting his feet in her mouth. Léolo begins to fantasize about Bianca sexually and discovers masturbation. Meanwhile, his brother Fernand, after being beaten by a bully and having failed a special education class, builds up muscles. Word Tamer, continuously monitoring Léolo's thoughts, reads the boy's hopes about how Fernand's muscles will make them invincible. However, upon being confronted by the bully for the second time, Fernand is overwhelmed with fear and is beaten again while Léolo watches in shock. Finally convinced his grandfather is responsible for all of the family's troubles, Léolo attempts to lower a noose and hang his grandfather while he is in the bath. His grandfather sees Léolo doing it and is choked, before finally being freed, with Léolo injured in the process. Léolo subsequently goes to the hospital, where he is told his actions could constitute attempted murder, though he is not charged. Reacting with horror to the ways other boys are pursuing sex, he seeks out the services of a prostitute named Regina. Upon later becoming ill, he ends up in the same institution where many other members of his family have been treated.

In 1966, various pirate radio stations broadcast to the United Kingdom from ships in international waters, specialising in rock and pop music not played on BBC Radio. Seventeen-year-old Carl, recently expelled from school, is sent to stay with his godfather Quentin, who runs the station Radio Rock anchored in the North Sea. The eclectic crew of disc jockeys and staffers, led by brash American DJ "The Count" and DJ "Doctor Dave". In London, government minister Sir Alistair Dormandy resolves to shut down pirate radio stations for their commercialism and immorality, instructing his subordinate Twatt to pursue legal stratagems to accomplish this. They attempt to cut off the pirates' revenue by prohibiting British businesses from advertising on unlicensed stations. Quentin counters by bringing massively popular DJ Gavin Kavanagh out of retirement on Radio Rock, enticing advertisers to pay their bills from abroad. Gavin's popularity creates a rivalry with The Count. Carl becomes smitten with Quentin's niece Marianne, but is heartbroken when she is seduced by Doctor Dave, while DJ "Simple" Simon Swafford marries glamorous fan Elenore in an onboard ceremony, but learns that she only married him to be near Gavin. The Count challenges Gavin to a game of chicken in defence of Simon's honour: The stubborn rivals climb the ship's radio mast to a dangerous height, but reconcile after they are both injured jumping into the ocean. Shortly after, Carl's mother Charlotte visits for Christmas, and denies that Quentin is his father. Carl gives her a cryptic message from reclusive late-night DJ "Smooth" Bob Silver, unexpectedly revealing that Bob is his father. Marianne arrives to apologise to Carl for sleeping with Dave, and she and Carl have sex. The following morning, the DJs announce news of the coupling to cheering fans across Britain. Meanwhile, Dormandy's vendetta against pirate radio advances when Twatt finds news of a fishing boat whose distress call was blocked by Radio Rock's powerful signal. Twatt proposes the creation of the Marine, &c., Broadcasting (Offences) Act 1967, making pirate radio stations illegal on the grounds that they endanger communication with other vessels. Despite heavy public support for the pirate stations, the act passes unanimously through Parliament and takes effect at midnight on 1 January 1967. The Radio Rock crew defy the law and continue broadcasting, firing up the ship's engine to evade arrest. The aging vessel's engine explodes, and the ship sinks. The DJs broadcast their position in hope of aid, and Twatt appeals to Dormandy to send rescue boats, but Dormandy refuses. Carl saves the oblivious Bob from his cabin while The Count vows to broadcast as long as possible. With the lifeboats inoperable, the crew gather on the prow as the ship goes down. They are rescued by dozens of fans in a fleet of small boats, with Carl being saved by Marianne. The Radio Rock ship disappears beneath the sea, with the Count emerging at the last moment.

Swedish efficiency researchers come to Norway to study Norwegian men, in an effort to help optimize their use of their kitchens. Folke Nilsson (Tomas Norström) is assigned to study the habits of Isak Bjørvik (Joachim Calmeyer). By the rules of the research institute, Folke has to sit on an umpire's chair in Isak's kitchen and observe him from there, but never talk to him. Isak volunteered for the program with the promise of a horse, but he only receives a dala horse, a little painted wooden statue. Isak stops using his kitchen and observes Folke through a hole in the ceiling instead. The two lonely men, observer and observed, slowly overcome the initial Norwegian-Swede and subject-observer distrust and become friends. Isak's friend Grant visits him often. Grant is a concentration camp survivor and feels Folke is stealing his friend. The friendship between Folke and Isak costs Folke his job during an inspection. He is forced to leave and drive up to the Swedish border, but then he returns, only to find Isak has died of a broken heart. Folke, now alone, occupies Isak's home and takes up Isak's friendship with Grant.

In 1961, the Men in Black (MIB) organization was founded after secretly making first contact with extraterrestrials. The MIB designates Earth as a neutral zone for alien refugees who live in secret among humans. Agents monitor alien activity and use memory-erasing neuralyzer devices to maintain secrecy. In 1997, MIB Agents K and D disrupt a border patrol operation at the Mexico–United States border to capture a Samurian named Mikey. When Mikey becomes violent, K uses a MIB gun to kill him and neuralyzes the patrol officers. D, feeling too old to continue, asks K to neuralyze him so he can retire. Soon after, NYPD officer James Darrell Edwards III apprehends a suspect, unaware that he is an alien. The alien warns of a coming threat before committing suicide. K, impressed by James' performance, recruits him into the MIB. After completing a series of tests, James becomes Agent J, and his previous identity is erased from public records. Meanwhile, a hostile alien known as a "Bug" crash-lands in upstate New York. The Bug kills a farmer named Edgar and uses his skin as a disguise. K and J, tipped off by a tabloid news article, question Edgar's wife. They learn that the Bug has killed two aliens who were living on Earth in disguise. Their bodies, along with their pet cat, are sent to a morgue overseen by coroner Laurel Weaver. At the morgue, the alien tells J and Laurel that "the galaxy is on Orion's Belt " before dying. After neuralyzing Laurel, K identifies the alien as Rosenberg, a prince from the Arquillian Empire. K and J visit Frank the Pug, an alien informant, who explains that Rosenberg was protecting a miniature galaxy. The galaxy is a powerful energy source that the Bug wants to use to destroy the Arquillians. An Arquillian warship soon arrives in Earth's orbit and demands that the MIB return the galaxy, or they will destroy the Earth. J and the Bug both realize the galaxy is on the collar of Rosenberg's cat, Orion, which is now with Laurel. The Bug captures her and swallows the galaxy. As the Arquillians prepare to destroy Earth to stop the Bug, the MIB locks down all transportation. J guesses the Bug will head to the New York State Pavilion, where the MIB hid flying saucers during the 1964-65 World's Fair. At the site, the Bug tries to escape with Laurel, but she briefly breaks free. K and J shoot down the ship, which crash-lands in Corona Park. The Bug sheds his human skin, revealing his true form and swallowing the agents' weapons. K allows himself to be eaten so he can retrieve his weapon from inside. J distracts the Bug until K shoots the Bug apart from within. Laurel uses J's gun to finish the Bug off. After returning the galaxy to the Arquillians, K reveals that he was training J to take his place. J neuralyzes him so he can retire. Later, J continues his work with Laurel, who has joined the MIB as Agent L.