Larry Kroger and Kent Dorfman seek to pledge a fraternity. Finding themselves ostracized at the prestigious Omega Theta Pi house party, the two visit the Delta Tau Chi house next door; Kent believes he cannot be rejected because his older brother Fred was a member, making him a "legacy." During the party, they meet the slovenly John Blutarsky ("Bluto"), chapter president Robert Hoover, smooth-talking Eric Stratton ("Otter") and his best friend Donald Schoenstein ("Boon"), motorcyclist Daniel Simpson Day ("D-Day"), and Boon's girlfriend Katy. Larry and Kent are accepted as Delta pledges and given the fraternity names "Pinto" and "Flounder," respectively. Delta is on probation due to campus conduct violations and poor academic standing. Wanting to remove the fraternity from campus, Dean Vernon Wormer directs Greg Marmalard, the smug Omega president, to find a justification for him to do so. Various incidents deepen the animosity between Delta, Omega, and Wormer, including the prank-related accidental death of a horse that belongs to Omega member and ROTC Cadet Commander Douglas C. Neidermeyer, who has been bullying Flounder, as well as Otter flirting with Marmalard's equally stuck-up girlfriend, Mandy Pepperidge. Bluto and D-Day steal the answer key to an upcoming psychology test from the trash, unaware that the Omegas have switched it for a fake. The Deltas all fail and their grade-point averages drop so low that Wormer tells them he needs only one more incident to revoke their charter and have them permanently dismissed from campus. To cheer themselves up, the Deltas organize a toga party and recruit Pinto and Flounder to shoplift food for it from a supermarket. There, Pinto meets a pretty young cashier named Clorette and invites her, while Otter invites Wormer's alcoholic, lecherous wife Marion. During the party, at which Otis Day and the Knights perform, Otter has sex with Marion, while Clorette makes out with Pinto until she passes out drunk. Pinto resists the temptation to have sex with her and instead takes her home in a shopping cart. He later discovers that she is the 13-year-old daughter of Carmine DePasto, the town mayor. Outraged by Marion's escapades and threatened with personal harm by DePasto, Wormer organizes a kangaroo court with the Omegas and revokes the Deltas' charter, confiscating the entire contents of their house. To clear their heads, Otter, Boon, Pinto and Flounder take a road trip in Fred's car. They visit an all-girls' college, where Otter