In the fall of 1962, Faber College freshmen Lawrence "Larry" Kroger and Kent Dorfman are seeking to join a fraternity. Finding themselves unwelcome at the exclusive Omega Theta Pi house party, the two visit the derelict Delta Tau Chi house next door. Kent believes that Delta will have to accept him as a "legacy" since his older brother was a member. They meet John ("Bluto") Blutarsky, chapter president Robert ("Hoov") Hoover, charismatic ladies' man Eric ("Otter") Stratton, motorcyclist Daniel Simpson ("D-Day") Day, Donald ("Boon") Schoenstein and Boon's exasperated girlfriend Katy. Larry and Kent are accepted as Delta pledges and given the fraternity names "Pinto" and "Flounder", respectively. Meanwhile, Omega pledge Chip Diller is accepted into the fraternity and given a paddling as part of his initiation. The Delta house is on probation due to regular shenanigans and overall poor academic scores. Wishing to remove the unruly fraternity from Faber's campus, Dean Vernon Wormer elevates the Deltas to "double secret probation" and directs Greg Marmalard, the Omega house president, to get fellow Omega and ROTC Cadet Commander Douglas C. Neidermeyer to find a reason to revoke Delta's charter. Various misadventures increase the rivalry between Delta, Omega, and Wormer, including the accidental death of Neidermeyer's horse during a retaliatory prank following the bullying of ROTC member Flounder by Neidermeyer. Unbeknownst to Marmalard, Otter has had an affair with Marmalard's girlfriend, Mandy Pepperidge, a member of the Alpha Delta Pi sorority. Bluto and D-Day steal the answers to an upcoming midterm exam, unaware the Omegas switched it for a fake. The Deltas all fail and their lowered grade-point averages prompt Wormer to announce he needs only one more misdemeanor to revoke their charter and permanently expel them. Undeterred, the Deltas organize a toga party and recruit Pinto and Flounder to shoplift from a supermarket as a fraternity prank. At the market, Pinto meets a young cashier named Clorette and invites her to the party, while Otter flirts with an older woman, who turns out to be Dean Wormer's alcoholic wife Marion. During the toga party, at which Otis Day and the Knights perform, Otter seduces Marion, while Pinto and Clorette make out until she passes out, drunk. Pinto resists the temptation to rape her while she is unconscious and instead delivers her home in a shopping cart. He later discovers that she is the 13-year-old daughter of Carmine DePasto, the corrupt mayor of the city of Faber who secretly takes advantage of Wormer. Wormer organizes a kangaroo court led by the Omegas, which revokes the Deltas' charter and confiscates the contents of their house. Otter, Boon, Pinto, and Flounder take a road trip in a Lincoln Continental Flounder has borrowed from his older brother, Fred. After reading about the recent death of a student at a nearby all-female college, Otter poses as her fiancé in order to find dates for himself and the others. The ruse works and the Deltas, along with their dates, stop at a club where Otis Day and the Knights are performing, unaware that the clientele is exclusively African-American. Some of the patrons intimidate the Deltas into abandoning their dates and fleeing the club, damaging both their car and several others in the parking lot. The next morning, Boon discovers Katy has spent the night with English professor Dave Jennings. Babs Jansen, herself in love with Marmalard, informs him that Mandy and Otter have been having an affair; Marmalard has Babs lure Otter to a motel where the Omegas ambush and assault him. Due to the Deltas' low midterm grades, Wormer expels them all from Faber and gleefully tells them he has notified their local draft boards that they are now all eligible for military service. The Deltas initially concede defeat until Bluto rallies the fraternity to seek revenge during the annual Homecoming parade. D-Day converts the heavily damaged Lincoln into an armored vehicle, which the Deltas conceal inside a cake-shaped breakaway parade float. The Deltas wreak havoc during the parade and crash into the reviewing stand, toppling the Wormers and DePasto. As Hoover asks the Dean for another chance, an epilogue amidst the chaos reveals the fates of the characters:

A group of photographs of the Stella Maris College 's Old Christians Rugby Team are seen as Carlitos Páez points out several members of the team and reflects on the accident in a brief monologue. Uruguayan Air Force Flight 571 flies over the Andes on October 13, 1972. The raucous rugby players and a few of their relatives and friends are eagerly looking forward to an upcoming match in Chile. Upon emerging from clouds, the plane encounters turbulence and collides with a mountain. The wings and tail are separated from the fuselage, which slides down a mountain slope before coming to a stop. Six passengers and one flight attendant are ejected from the plane and die. Antonio, the team captain, coordinates efforts to help the injured. Roberto Canessa and Gustavo Zerbino, both medical students, aid the injured. Another six passengers soon die, including both pilots and Nando's mother, Eugenia. Nando, who sustained a head injury, falls into a coma, and his sister Susana has suffered severe internal injuries. As the sun sets, the survivors make preparations for the night. Canessa discovers that the seat covers can be unzipped and used as blankets. The survivors go inside the fuselage and curl up beside one another to stay warm. Antonio, Roy Harley, and Rafael Cano plug the gaping hole at the end of the fuselage with luggage to keep out the wind. Two passengers die overnight. With nothing to hunt or gather on the mountain, Antonio declares they will use rationing when the survivors find a tin of chocolates and a case of wine. After seeing a plane fly past, they think it dipped its wings, and the survivors celebrate. Expecting to be rescued the next day, everyone except Javier, his wife Liliana, and Antonio finish the remaining chocolates. This causes a quarrel among Antonio and several others. Nando regains consciousness. After learning of his mother's death, Nando watches over Susana vigilantly. Knowing she will die of her injuries within a few days, he vows to set off on foot and find a way out of the mountains. When Carlitos reminds him that he will need food, Nando jokingly suggests eating the flesh of the deceased pilots to give him the strength to survive the journey to find help. Susana dies from her injuries. The survivors listen to a radio for word of their rescue but are devastated to hear that the search is to be called off after nine days. After great debate, the starving passengers decide to eat the flesh of their dead relatives and friends. Zerbino, Rafael, and Juan Martino set off to search for the tail of the plane in hopes of finding batteries for the plane's radio to transmit their location. Among pieces of the wreckage, the teammates find additional corpses, but return to the group with news that the tail of the plane is likely a little further away. Later in the week, an avalanche strikes the plane and fills much of the interior with snow. Eight of the survivors, including Antonio and Liliana, are smothered to death by the snow. The remaining 19 survivors are forced to stay inside the plane when they realize there is a blizzard outside. A second team, made up of Nando, Canessa, and Antonio "Tintin" Vizintin, sets out and finds the tail of the plane. Unable to bring the batteries to the fuselage, they return to the fuselage to get Roy, who is thought to have experience with electrical equipment. They bring him to the tail of the plane to see if he can fix the radio. When Roy is unsuccessful, the team decides to return to the fuselage. Federico and Alberto die from their injuries, as does Rafael, leading Nando to convince a reluctant Canessa to search for a way out of the mountains, taking Tintin with them. Two days into the journey, they send Tintin back to the fuselage so they can appropriate his rations and continue on their own. After a 12-day trek, the two escape the mountains and alert the authorities to their companions' location. Two helicopters, one of which has Nando and Canessa on board, appear overhead of the survivors on the mountain, leading the remaining 14 survivors to celebrate their impending rescue. In the present, Carlitos describes how a group later returned to the site of the crash and buried the corpses under a pile of stones, marked with a cross. The memorial to the 29 deceased and 16 survivors is shown.

Teachers Martin, Tommy, Peter, and Nikolaj are colleagues and friends who work at a gymnasium school in Copenhagen. All four struggle with unmotivated students and feel that their lives have become boring and stale. Martin is confronted by his senior students and their parents, who express that he has become a barrier to their passing their history exams. At a dinner celebrating Nikolaj's 40th birthday, the group discusses a theory inspired by the work of psychiatrist Finn Skårderud —that humans are born with a blood alcohol content (BAC) deficiency of 0.05% and that maintaining a BAC of 0.05% makes one more creative and relaxed. The friends decide to embark on an experiment to test Skårderud's theory. They start a group log documenting their experiences as they drink at regular intervals to maintain this blood alcohol level. Two of them have personal struggles that make the experiment particularly appealing: Martin is depressed and alienated from his family and students, while Nikolaj's wife seems to have contempt for him. They agree on a set of rules: their BAC should never drop below 0.05% during the day on weekdays, and they should not drink after 8:00 p.m. or on weekends. Each man finds his own way to sneak alcohol during the day while teaching or coaching children, but they never drink and drive, with 0.05% being the legal limit. Within a short period, all four men find their work and private lives more enjoyable and successful. Martin, in particular, is delighted as he reconnects with his wife and children. His teaching becomes inspired, and his students begin enjoying class and respecting him. He even incorporates alcohol into his history lessons, engaging his heavy-drinking students. Encouraged by their success, the group decides to take the experiment further, increasing their BAC minimum to 0.10%. Still feeling the benefits, they eventually push the boundaries further, deciding one night to drink to oblivion to test its liberating effects. However, after returning home incapacitated, both Martin and Nikolaj are confronted by their families. Martin's family expresses concern, revealing they have known he has been drinking for weeks. He and his wife acknowledge their growing distance, and she admits to infidelity. Martin lashes out and leaves, heading to Tommy's. The group abandons the experiment. Martin and his wife separate, and, when he tries to make amends, she rejects him. All members of the group stop drinking during the day, except for Tommy, whom the others try to support. However, at a faculty meeting where the headmaster reveals that teachers have been drinking at work, Tommy arrives visibly intoxicated. Later, he boards his boat while drunk, takes his old dog with him, motors out onto the bay, and ultimately goes overboard, drowning at sea. After Tommy's funeral, the three remaining friends go out to dinner to celebrate his life, enjoying sparkling wine. While dining, Martin receives a text from his wife saying she misses him. As they sit by the harbour, recently graduated students pass by, celebrating in their customary drunken revelry. Martin, Peter, and Nikolaj join them in drinking and dancing. Martin, a former jazz ballet dancer, finally gives in to his colleagues' previous urgings and dances with the students. His movements grow increasingly energetic and joyous before he finishes his dance by spontaneously jumping into the sea.