Four radicalised British Muslim men living in Sheffield (three of whom are British Pakistani) aspire to become suicide bombers: Omar, who is deeply critical of Western society and interventionism; his dim-witted and anxious cousin Waj; Barry, a bad-tempered and rash English convert; and the naive Faisal. When Omar and Waj travel to an al-Qaeda -affiliated training camp in Pakistan, Barry recruits a fifth member, Hassan, after witnessing him pretending to commit a suicide bombing at a conference. The training in Pakistan ends in disaster when Omar accidentally destroys part of the camp attempting to shoot down a suspected drone; the pair are forced to flee. Omar later uses the experience to assert authority on the group on his return to Britain. The group disagrees about what the target should be. Barry wants to bomb a local mosque as a false flag operation to "radicalise the moderates" and Faisal suggests blowing up a Boots because it sells contraceptives. Ahmed, Omar's conservative, pacifist brother, tries to talk him out of doing anything violent; however, Omar and his wife, Sofia, mock Ahmed for his unwillingness to be in the same room as a woman, and accuse him of keeping his wife in a cupboard. Sofia instigates a water gun fight with him, prompting Ahmed to leave in a huff. After the group begins production of the explosives, Hassan is left to watch the safehouse as Barry, Waj and Faisal test detonate a small amount of TATP contained in a microwave, using a nearby fireworks show to cover the sound. When they return, they find Hassan dancing with an oblivious neighbour. The group suspects they have been compromised and transport the explosives to a new location in grocery bags. Faisal trips up while crossing a field and is killed in the explosion. This angers Omar, who berates the others and leaves. Faisal's head is found, tipping off the authorities, and Omar tells the others and they reconcile. Omar decides to target the upcoming London Marathon due to having access to mascot costumes, which they use to conceal the bombs. Meanwhile, armed police raid Omar's brother's house. At the Marathon, Waj expresses doubts about the morality of their plot, but Omar convinces him to go through with it. A police officer approaches the group, which leads Hassan to attempt to alert the officer about their plot, but is killed when Barry remotely detonates his bomb. The remaining three panic and run away as the police search for them. Omar has a change of heart, feeling guilt about manipulating Waj into dying for a cause he does not understand and attempts to prevent the attack. Two police snipers receive Omar's description, a man dressed as the Honey Monster, but one of them mistakenly kills a bystander in a Wookiee costume. Waj is cornered by police in a kebab shop and takes the staff hostage. Omar calls Waj and convinces him to let all but one of the hostages go. Barry finds Omar, snatches his phone, and swallows the SIM card. However, as Barry begins to choke, a well-meaning passer-by attempts to perform the Heimlich manoeuvre, forcing Omar to flee before Barry's bombs are inadvertently detonated. Omar hurries to a nearby phone store to buy a new SIM card to contact Waj but leaves empty-handed. He spots a colleague and borrows his phone. Omar attempts to talk Waj down, but his call is interrupted when the police charge in and kill the remaining hostage, whom they mistake for Waj. Waj's bomb is then detonated, killing everyone in the kebab shop. Distraught, Omar walks into a nearby pharmacy and detonates his own bomb. In an epilogue, it is revealed the police later arrested Omar's innocent brother as a terrorist and abducted him to a black site; that they deflect responsibility for shooting the hostage and the bystander; and that Omar unknowingly killed Osama bin Laden when misfiring the rocket in Pakistan.

The residents of Sunnyvale Trailer Park attend the funeral of Ricky 's father Ray, who is believed to have died in a propane explosion. Trailer park supervisor Jim Lahey and his partner Randy attend the service, despite being uninvited; the pair are forced to leave after Lahey expresses his belief that Ray is still alive. Ricky has purchased a house in a subdivision where he keeps an upscale marijuana growing operation. Lahey has recently suffered a stroke, which he blames Ricky for, and vows to get revenge. With the help of his lackey Jacob Collins who is now serving in the Canadian Army, Julian has developed a new money-making scheme in selling drug-tested urine. Bubbles has been living under J-Roc and Sarah 's trailer step for two years due to not being able to find work. J-Roc and Sarah later plan an intervention and tell Bubbles to move out. While Bubbles is packing his things, he receives a letter from Randy which he hangs on to. Bubbles is later attacked by thugs while delivering chicken and sent to the hospital. Julian warns Ricky that with the potential legalization of marijuana, his growing operation business will become obsolete. Ricky refuses to work for Julian and vows to go to Parliament Hill in Ottawa to protest the upcoming legal action. After visiting Bubbles at the hospital, Julian asks him to work for him. Bubbles accepts the offer after revealing that his letter was from a lawyer saying that his deceased parents left land and a house for him in Kingston. Julian promises to take Bubbles to the place after they finish the job. Jacob later reveals that he has been dishonorably discharged from the Army. After Jacob's father Phil rages at Julian, Bubbles, and Tyrone — who recently ran away from a halfway house — the three steal Phil's food truck, "The Dirty Burger", and make their way to the urine deal, with Julian letting Bubbles drive a separate van. Bubbles then offers Ricky a ride to Ottawa after the transmission in Ricky's car fails. Lahey and Randy secretly follow the boys on their trip, with the intent of planting cocaine in their vehicles and framing them. While on the drive, Lahey tries some of the cocaine and quickly becomes addicted, which worries Randy. While Bubbles and Ricky are driving in the van, they drive by the now burned down Dirty Burger and watch as police arrest Tyrone; they pick up Julian before the police can find him. Later, Bubbles purposely drives past the turnoff to Montreal where the deal is supposed to happen. When Julian finds out, Bubbles admits that he does not want to be a part of the scheme anymore, and just wants to go to his parents' land. Once they get there, it is revealed that the home of Bubbles's parents is a rundown bus parked next to a lake. Bubbles opts to live there, despite Ricky and Julian's protests; however, at the last minute, he decides to go back with them. Once they arrive at Montreal, Bubbles and Ricky go to a strip club while Julian waits for his customers; he is then robbed by his arch-rival Cyrus and his accomplices Dennis and Terry. Randy calls the bomb squad on Julian's van, and they discover cocaine in the wheel well. Julian is arrested, but Bubbles and Ricky manage to get away. After finding Lahey and Randy, Bubbles steals their car and drives Ricky to Ottawa. Once at Parliament Hill, Ricky sneaks his way into the building and makes an outrageous speech which gets him pulled out by security. A lawyer then offers to help get him out of jail quickly and obtain a marijuana license. While a police officer takes Ricky and Bubbles away, Lahey, highly intoxicated on liquor and cocaine, knocks the officer unconscious and fights a handcuffed Ricky. After the officer regains consciousness, he tases Lahey. Now in jail, Lahey reveals that the taser shock reversed his stroke. He is no longer using cocaine and has started a relationship with his cellmate. Bubbles has his parents' bus taken to Sunnyvale where he now resides. Julian has stopped dealing drug-tested urine and has started a relationship with an unnamed woman. Randy has revealed that he is over Lahey and has gone back to hooking. Ricky reveals that his marijuana growing operation is a success, since he is now able to sell marijuana legally. He receives a letter containing a VHS tape, which reveals that his father Ray is still alive and now living in a landfill site in Florida, having performed a life insurance scam.

In London, mob boss Lenny Cole rules the ever-growing real estate business, using a corrupt councillor for bureaucratic fixing, and his right-hand man Archy for the dirty side of things. A billionaire Russian businessman, Uri Omovich, plans a fixed land deal, and London's crooks all seem to want a piece of it — particularly Uri's underhanded accountant Stella, and a gang called "The Wild Bunch" led by small-time crook "One-Two", his partner "Mumbles", and their driver "Handsome Bob". Uri agrees to Lenny's price of €7,000,000 for bribing the council, and as a sign of trust, lends him his "lucky painting". Yet when Uri arranges for Stella to move the funds, she double-crosses him and hires the Wild Bunch to steal the money. Additionally, Lenny's estranged and drug-addicted stepson Johnny Quid steals the painting from Lenny's office after faking his own death. Lenny and Archy then coerce Johnny's former talent managers Mickey and Roman into tracking down Johnny. In a subplot, Handsome Bob gets close to Stella's gay husband, a lawyer who has information on a longtime unknown informant in their criminal circle, and asks One-Two for a single dance before Bob goes to prison after the informant exposed him. Uri tasks Stella once more with covertly siphoning the necessary payoff from his holdings, despite his growing suspicion of her. Yet when his moneymen are once again robbed by the Wild Bunch, his assistant Victor convinces him that Lenny is likely to be behind the robberies, and is also purposely keeping Uri's lucky painting from him. Uri and Victor then invite Lenny to a private golf game, where Victor beats him with a golf club, finishing by breaking Lenny's leg as a warning to return his painting. Wild Bunch friend Cookie happens to buy the painting from a couple of crackheads who stole it from Johnny's hideout. Cookie then gives the painting to One-Two, who in turn offers it to Stella as a token of appreciation after a sexual encounter. After Stella leaves his flat, One-Two is surprised by Uri's henchmen but is rescued, and subsequently kidnapped, by Archy and his goons, who had come looking for Uri's money. Uri wants to marry Stella, whom he has long admired. He goes to Stella's house to propose, but he then spots the painting. Stella lies and says she has had it for years. Uri, enraged by Stella's betrayal, orders Victor to kill her. Archy brings Johnny, Roman, Mickey and the Wild Bunch to Lenny's warehouse where Lenny orders Johnny and the Wild Bunch executed. Handsome Bob offers the legal documents concerning the informant in his pocket to Archy. Archy recognizes the pseudonym used on documents, "Sidney Shaw", as belonging to Lenny. Lenny had arranged with the police to routinely lock up many criminal associates (including Archy) for years at a time to ensure his own freedom and while also enhancing his own standing in the criminal underworld. Archy orders Lenny's men to free the Wild Bunch and has Lenny drowned and fed to crayfish. In the elevator, Johnny explains to Roman and Mickey that they will also be killed to leave no witnesses, and graphically explains the manner of their executions. His description unnerves the man tasked to execute the trio, prompting him to act prematurely. Having already anticipated this move, Johnny warns Mickey and Roman to intervene and kill their would-be executioner. Johnny shoots two more men waiting at the top of the elevator and with help from the Wild Bunch, they escape the last of Archy's men. Later, Archy picks up Johnny from rehab and gives him Uri's lucky painting as a welcome home present, remarking that obtaining the painting "cost a very wealthy Russian an arm and a leg". Johnny proclaims that, with his new-found freedom from addiction and his stepfather, he will do what he could not do before: "become a real RocknRolla". In a post-credit scene, One-Two accedes to Handsome Bob's request to dance with him.

Okwe, a doctor in his home country (not initially named) who was forced to flee after being falsely accused of murdering his wife, lives in the United Kingdom as an undocumented immigrant. He drives a cab in London during the day and works at the front desk of a hotel at night, which is staffed by other immigrants, both documented and undocumented. He is pressed to treat other poor immigrants, including fellow cab drivers with venereal diseases, with scarce supplies provided by his friend Guo Yi, an employee at a hospital mortuary. Juliette, a sex worker who regularly conducts her business at the hotel, informs Okwe about a blocked toilet in one of the rooms, and he fishes out a human heart. The manager of the hotel, Juan, runs an illegal operation at the hotel wherein immigrants swap kidneys for forged passports. After learning of Okwe's past as a doctor, Juan pressures him to join his operation as a surgeon, but Okwe refuses. Senay is a Turkish Muslim seeking asylum who also works at the hotel as a cleaner. Her immigration status allows her to stay in the UK, provided she does not work; the hotel is a perfect cover because she is not named on its books. She allows Okwe to sleep on her sofa when she is not home, as she is from a conservative culture where men and women who are not married do not spend the night together under the same roof. After Senay is visited by Immigration Services, who inspect the hotel after finding a book of matches in her flat, Okwe prevents the officials from intercepting her. No longer able to work at the hotel, Senay begins working in a sweatshop making clothes, which is also raided by officials looking for undocumented immigrants, who the manager gets rid of. The manager allows Senay to keep her job and not report her to the authorities in return for her performing oral sex on him; she initially complies before proceeding to bite him. Okwe finds her a place to stay at the hospital mortuary, while Senay asks him to accept Juan's proposition in his organ business to raise money to travel to America. In desperation, Senay offers her kidney to Juan for a passport; Juan accepts the deal on condition he takes her virginity as well. Senay is later provided with a morning-after pill by Juliette. After learning of Senay's plan, Okwe agrees to perform the operation to ensure her safety, but only if Juan provides them both with passports under different names. After Juan delivers the passports, Okwe and Senay drug him, surgically remove his kidney, and sell it to Juan's contact. Okwe plans to use his new identity to return to his young daughter in Nigeria, and Senay plans to start a new life in New York. Before they part at Stansted Airport, they mouth the words "I love you" to each other, and she gives him her cousin's address in New York. Senay boards her plane, and Okwe calls his daughter long-distance to tell her he is finally coming home.

An ancient Buddha statue named Ong-Bak is kept in the village of Ban Nong Pradu in rural northeastern Thailand. The villagers fall in despair after thieves from Bangkok desecrate the statue Ong-Bak and take the head with them. Ting, a resident and Muay Thai expert, volunteers to travel to Bangkok to recover the stolen head. Ting's only lead is Don, a drug dealer who attempted to buy an amulet in Nong Pradu earlier. Upon arriving in Bangkok with a bagful of money donated by the village, Ting meets his cousin Humlae, who has dyed his hair blond and begun calling himself "George." Humlae and his friend Muay Lek are street-bike racing hustlers who make a living out of conning yaba dealers. Reluctant to help Ting, Humlae steals Ting's money and bets it in an underground fighting tournament at a bar on Khaosan Road. Ting tracks down Humlae and gets his money back after stunning the crowd by knocking out the champion, where his extraordinary skill grabs the attention of Komtuan, a grey-haired crime lord who uses a wheelchair and needs an electrolarynx to speak. Don is the one who ordered Ong-Bak's head stolen to sell it to Komtuan, who sees no value in it and orders him to dispose of it. The next day, Humlae and Muay Lek are chased all over town by drug dealer Peng and his gang after a botched baccarat game scam at an illegal street gambling booth. Ting fights off most of the thugs and helps Humlae and Muay Lek escape in exchange for helping him find Don. They return to the bar, where Ting wins the respect of the crowd after defeating three opponents consecutively. The trio find Don's hideout, triggering a lengthy tuk-tuk chase. The chase ends at a port in the Chao Phraya River, where Ting discovers Komtuan's cache of stolen Buddha statues submerged underwater. After the statues are recovered by police, Komtuan sends his thugs to kidnap Muay Lek and tells Humlae to ask Ting to fight his bodyguard Saming near the Thai- Burmese border in exchange for Muay Lek and the Ong-Bak head. Ting is forced to throw the match against the drug-enhanced Saming, and Humlae throws in the towel. After the fight, Komtuan reneges on his promise to release Muay Lek and return the head, where he orders his henchmen to kill the trio. Ting and Humlae subdue the thugs and head to a mountain cave, where Komtuan's men are cutting a giant Buddha statue. Ting defeats the remaining thugs and Saming but is shot by Komtuan, who attempts to destroy the Ong-Bak head with a sledgehammer. Humlae protects it with his body, taking the brunt of the hammer blows. The giant Buddha statue head suddenly falls, crushing Komtuan to death and critically injuring Humlae. With his dying breath, Humlae gives the Ong-Bak head to Ting and asks him to look after Muay Lek. The head is returned to Ban Nong Pradu. Humlae's ashes, carried by an ordained monk, is brought to the village in a procession on an elephant's back while the villagers, Ting and Muay Lek celebrate the return of Ong Bak's head.

At a bistro in Montmartre, IRA operative Deirdre meets with two Americans, Sam and Larry, and a Frenchman, Vincent. She takes them to a warehouse where Englishman Spence and German Gregor are waiting. Conversations among the men reveal that they are former government and military agents who have become mercenaries. Deirdre briefs the group on their mission: to attack a heavily armed convoy and steal a large, metallic briefcase, whose content is never revealed. The team's first preparation task is to acquire firearms, which turns into an ambush; the team survives and gets the weapons. Deirdre meets with her handler, Seamus O'Rourke, who tells her that the Russian mafia is bidding on the briefcase and that the team must intervene to prevent them from winning. Spence is exposed as a fraud by Sam; he is dismissed by Deirdre, and the others continue their mission. Deirdre's team successfully ambushes the convoy at Villefranche-sur-Mer and pursues the survivors to Nice. During the gunfight, Gregor steals the case and replaces it with explosives in an attempt to sabotage the others. He attempts selling it to the Russians, but his contact betrays him; Gregor kills the contact and has Mikhi – the Russian mobster in charge of the deal – agree to another meeting. The team tracks Gregor through one of Sam's old contacts and corners him in the Arles Amphitheatre during his meeting with two of Mikhi's men. Sam chases Gregor, who flees but is caught by Seamus. Deirdre and Vincent confront the two Russian hoods, prompting a shootout. Sam arrives to help, killing one, but is injured by a ricochet from the other. Seamus kills Larry and escapes with a reluctant Deirdre and the captured Gregor. Vincent takes Sam to a villa that is owned by his friend Jean-Pierre. After removing the bullet and letting Sam recuperate, Jean-Pierre compares Sam's situation to the tale of the 47 Ronin. Vincent asks Jean-Pierre to help them find Gregor and the Irish operatives. In Paris, Gregor is persuaded through violent interrogation to return the case to Seamus and Deirdre. After retrieving it from a post office, they are pursued by Sam and Vincent in a high-speed chase. Vincent shoots out their tire, sending their car off an overpass. Gregor escapes with the case while road workers rescue Deirdre and Seamus from the burning vehicle. Doubtful of where to go next, Sam and Vincent decide to track down the Russians after discovering that the decoy case that Gregor used in his theft of the original is used for carrying ice skates; one of Jean-Pierre's contacts informs them that the Russians may be involved with figure-skater (and Mikhi's girlfriend) Natacha Kirilova, who is performing at Le Zénith. During Natacha's show, Mikhi meets with Gregor, who says that a sniper in the arena will shoot Natacha if Mikhi betrays him. Mikhi kills Gregor and takes the case, allowing Natacha to be killed by the sniper. Amid the ensuing chaos from Natacha's shooting, Sam and Vincent leave the arena in time to see Seamus kill Mikhi and steal the case. Sam and Vincent split up; Vincent pursues Seamus but is wounded in a gunfight. Sam finds Deirdre waiting in a getaway car and convinces her to leave, after explaining that he is still in the CIA and is after Seamus, not the case. As she drives away, Seamus is forced to return to the arena as Sam gives chase. Seamus ambushes Sam but is shot dead by Vincent before Seamus can kill Sam. Sam and Vincent have coffee in the bistro where they first met. A radio broadcast announces that a peace agreement between Sinn Féin and the British government has been reached, partially as a result of Seamus's death. Sam keeps glancing at the door as patrons enter, but Vincent convinces Sam that Deirdre will not be coming back. They shake hands and part ways, but not before Vincent asks what was in the case. Sam replies that he does not remember. Sam drives off with his CIA contact as Vincent pays the bill and leaves.

As 1999 nears its end, Los Angeles has become a dangerous war zone. A Chinese restaurant is robbed by a group of criminals, with one recording the event with a SQUID (Superconducting QUantum Interference Device), an illegal electronic device that records memories and physical sensations directly from the wearer's cerebral cortex onto a MiniDisc -like storage device. Lenny Nero, a former LAPD officer turned black marketeer of SQUID recordings, buys the robbery clip from his main supplier Tick. Elsewhere, Iris, a prostitute and former friend of Faith Justin (Lenny's ex-girlfriend), is chased by LAPD officers Burton Steckler and Dwayne Engelman. Iris escapes on a subway car, but Engelman pulls off her wig, revealing a SQUID recorder headset. Lenny pines for Faith and relies on emotional support from his two best friends—Max Peltier, a private investigator, and Lornette "Mace" Mason, a bodyguard and limousine driver. Mace has unrequited feelings for Lenny from when he was still a cop and acted as a father figure for her son after her boyfriend was arrested on drug charges, but disapproves of his SQUID-dealing business. While Lenny and Max are drinking at a bar, Iris drops a SQUID disc through the sunroof of Lenny's car before it is towed away. Mace picks Lenny up and takes him to a nightclub where Faith is going to sing. There, Lenny receives a SQUID disc from an anonymous contact and unsuccessfully tries to get Faith away from her new boyfriend, Philo Gant. Philo is a music industry mogul who managed the recently murdered rapper Jeriko One. While in the car with Mace, Lenny plays the disc the contact gave him and watches as Iris is brutally raped and murdered by an attacker at the Sunset Regent hotel. As they approach the hotel, Iris's body is taken out on a stretcher. The next day, they take the disc to Tick, who cannot identify the source of the recording, but recalls that Iris was looking for Lenny. Deducing Iris may have left something in Lenny's car, Mace and Lenny go to the impound and find Iris's disc. Steckler and Engelman appear and demand the disc at gunpoint, but Lenny and Mace escape in her bullet-resistant car before being forced to stop at a dock. Steckler pours gasoline on the car and sets it on fire, but Mace drives it into the harbor, extinguishing the flames. When they reach the surface, the cops have left. Mace takes Lenny to her brother's house, and they watch Iris's disc, showing Iris was with Jeriko One when Steckler and Engelman pulled him over and murdered him, because his anti-police lyrics and activism incited protests against the LAPD. The two return to Tick, who Max explains has been rendered brain-dead from forceful exposure to amplified SQUID signals. Lenny fears Iris's attacker covered his tracks by "killing" Tick and will come after Faith. Back at the nightclub, Lenny and Mace confront Faith, who reveals that Philo is afraid Iris's disc would reveal that he kept his artists under surveillance. Lenny and Mace disagree over whether to trade the disc to Philo for Faith's freedom or release it publicly, which could incite a citywide riot. As midnight approaches, Lenny and Mace sneak into a private party that Philo is hosting at the Westin Bonaventure Hotel for the city's wealthy elite. Lenny has a change of heart and tells Mace to give the disc to deputy police commissioner Palmer Strickland. In Philo's penthouse suite, Lenny finds Philo brain-dead on the floor and another disc, revealing Faith's affair with Max, who "fried" Philo's brain with an amplified recording of them feigning rape. Pointing a gun at Lenny, Max explains that Philo hired him to kill Iris, but when Philo wanted Faith dead as part of the coverup, he decided to frame Lenny for the murders. Lenny and Max struggle in a fight, Faith intervenes and pulls off Max's wig with a SQUID inside - assuring a confession - and Max stabs Lenny in the back. The fight culminates with Lenny on the balcony with Max hanging over; Lenny pulls the knife from his back to cut his necktie and drop Max to his death. Lenny goes downstairs to find Mace, leaving Faith standing alone on the balcony. Meanwhile, on the crowded streets, Mace subdues Steckler and Engelman with baton and taser, but other officers take down Mace. The crowd moves in, in support of Mace, and a major riot seems inevitable. Strickland, who has viewed Iris's disc, arrives and orders Mace's release and the arrest of Steckler and Engelman for murder. Engelman commits suicide; Steckler threatens Mace, but the officers gun him down. Lenny finds Mace, and the two share a hug before she gets in Strickland's car. Then Lenny drags her out, and they share a kiss as the crowd celebrates the turn of the new millennium.

When 17-year-old Tanja Lorentzen is found murdered in the city of Tromsø, far up in the Norwegian Arctic, Kripos police officers Jonas Engström (Stellan Skarsgård) and Erik Vik (Sverre Anker Ousdal) are called in to investigate. Engström, formerly with the Swedish police, moved to Norway after being caught having sex with the main witness in one of his cases. Vik is nearing retirement age, and his memory is failing. Engström devises a plan to lure the murderer back to the scene of the crime, but the stakeout is blown and the suspect flees into the fog, shooting one of the Norwegian police officers in the leg. Unbeknownst to his unarmed colleagues, Engström carries a gun from his days in the Swedish police, who routinely carry firearms. Firing at what he believes to be the suspect, Engstrom accidentally kills Vik, who had mistakenly run right instead of left as ordered. Realizing that everyone assumes Vik was shot by the fugitive, Engström decides not to admit his culpability. When one of his colleagues, Hilde Hagen (Gisken Armand), is assigned to investigate Vik's death, Engström becomes worried about ballistic fingerprinting and tampers with evidence to support his story. Haunted by guilt and unable to sleep with the midnight sun of the Arctic, Engström becomes increasingly unhinged and starts hallucinating about Vik. Engström learns from one of Tanja's friends that she had been seeing Jon Holt (Bjørn Floberg), a crime novelist. He correctly deduces that Holt killed Tanja, but Holt reveals that he saw Engström shoot Vik. The two decide to frame Tanja's boyfriend Eilert for her murder, with Engström later planting Holt's gun under Eilert's bed and Holt giving testimony about Eilert being abusive. However, Hagen is not convinced, and when new evidence emerges, Engström knows that it is only a matter of time until Holt is arrested. Engström tracks Holt to some waterfront properties that are slowly collapsing into the sea. Holt suspects that Engström has come to kill him and holds him at gunpoint, explaining how he killed Tanja in a fit of rage when she rejected his advances. Holt tries to flee across a pier, but the rotten floorboards give way and he falls into the water below, striking his head on the way down. He drowns as Engström watches. When Engström searches Holt's nearby house, he finds Tanja's dress, which Holt had removed before dumping the body. With Holt dead, and definitive proof he was the murderer, the case is closed. Just before he leaves town, Engström is visited by Hagen, who shows him a cartridge case found at the site where Vik was shot. She notes it is a Norma, which Engström confirms is a brand used by the Swedish police. Engström expects Hagen to arrest him, but instead she simply places the cartridge on a table and leaves. Engström drives out of town, his face and eyes showing great weariness, and he seems not to have recovered from his insomnia.

In 2005, unpopular-yet-scholarly student Morton Schmidt and popular-yet-underachieving athlete Greg Jenko miss their school prom, Schmidt being rejected by the girl he was trying to ask to be his date and Jenko being barred from attending due to failing grades. Seven years later, the duo meet again at the police academy and become friends. After graduating, the two become partners assigned to bicycle patrol at the local park. They catch a break when they arrest Domingo, the leader of a one-percenter motorcycle gang for drug possession, but are forced to release him after they fail to read him his Miranda rights. The duo is reassigned to 21 Jump Street, a revived undercover program from the 1980s, which specializes in infiltrating high schools. Captain Dickson assigns them to contain the spread of a newly-made synthetic drug called HFS ("Holy Fucking Shit") at Sagan High School. He gives them new identities and enrolls them as students, giving them class schedules fitting their previous academic performances; Jenko taking mostly arts and humanities, and Schmidt taking mostly science classes, but the duo mix up their identities. Schmidt gets a lead on HFS from classmate Molly, and he and Jenko meet the school's main dealer, popular student Eric. The two take HFS in front of him to maintain their cover, and then rush to the bathroom and attempt to vomit the HFS out of their systems, but are unsuccessful. Eric takes a liking to Schmidt, who develops a romantic interest in Molly. Jenko becomes friends with the students in his AP Chemistry class and finds himself becoming more interested in geeky hobbies and academic pursuits. Schmidt and Jenko throw a party at Schmidt's parents' house, where they are living during the course of their assignment, and invite Eric. During the party, a fight breaks out between Schmidt, Jenko, and some party crashers from another high school. Schmidt wins the fight, impressing Eric and gaining his trust. Jenko's friends hack Eric's phone to enable them to listen in on his conversations. The phone hack reveals information about an upcoming meeting between Eric and his supplier. Jenko happens to overhear conversations between Schmidt and Eric, where he catches Schmidt making disparaging comments about him. A rift between the duo grows and their official police work suffers. Schmidt and Jenko later track Eric to a cash transaction with the distributors of HFS—the motorcycle gang from the park—and a chase ensues on the freeway. They return to school, argue, and eventually begin fighting, which disrupts the school play. They are expelled from school and fired from the Jump Street program. Eric, stressed and terrified, recruits Schmidt and Jenko as security for a deal taking place at the school prom. While dressing for the prom, Schmidt and Jenko rekindle their friendship. At the prom, Schmidt is forced to reveal his identity as a cop, upsetting Molly. When they go to the penthouse, they discover that the supplier is the physical education teacher, Mr. Walters, who created the drug accidentally and started selling it to the students to supplement his teacher's salary and pay alimony to his ex-wife. Having caught Eric smoking marijuana, he was able to persuade him to be his dealer. The motorcycle gang arrives for the deal, but Molly, high on HFS, interrupts them and starts arguing with Schmidt, outing him as a police officer. As a result, gang leader Domingo recognizes Schmidt and Jenko and orders his men to kill them. Two of the gang members then reveal themselves to be undercover DEA agents Tom Hanson and Doug Penhall, former members of the Jump Street program. In an ensuing exchange of gunfire, Hanson and Penhall are both mortally wounded. Mr. Walters and Eric escape with the money and Molly as a hostage; the gang, Schmidt, and Jenko follow close behind. Jenko creates a homemade bomb and uses it to kill the gang. Mr. Walters shoots at Schmidt but Jenko takes the bullet to his arm, sparing Schmidt's life. In response, Schmidt shoots Mr. Walters, unintentionally severing his penis. They arrest Mr. Walters and Eric, successfully reading the former his Miranda rights. Schmidt and Molly share a kiss while Eric and Mr. Walters get arrested. Both officers are congratulated and reinstated in the Jump Street program as Dickson gives them a new assignment: infiltrating a college.