Jeff Chang, Justin Chon, and his best friends Casey Skylar Astin and Miller Miles Teller are set to celebrate Jeff’s 21st birthday, a milestone that lands on the night before a crucial medical school interview. Casey and Miller, who are already 21 or over, hope to give Jeff one last night of carefree fun, but Jeff initially declines. When Miller threatens to make a ruckus all night if Jeff doesn’t join, Jeff agrees to come along for just one drink.
In the bar, Jeff accidentally strikes a boy named Randy, Jonathan Keltz, with a dart. Randy becomes aggressive, and the trio has to flee, even as Casey is enjoying a promising conversation with a girl named Nicole Sarah Wright. Jeff overindulges and becomes unresponsive, and Casey and Miller struggle to get him home, only to realize they don’t remember where he lives.
Nicole knows Jeff, so they seek her help to track down the address. They sneak into a sorority house they believe hosts Nicole, only to discover it’s the wrong one—filled with Latina students. The house erupts with fury when the intrusion is revealed, and the pair scramble to escape. In the chaos, Casey and Miller push Jeff from a balcony onto a pool cover, which bounces him into a rose garden; they fear they’ve killed him, but he survives with only thorn pricks in his buttocks.
They locate Nicole, but she doesn’t know the address and sends them to Randy for help. Randy refuses to look up the information, so Miller, threatening him with a gun found on Jeff, coerces him to help steal a phone. A shot into the air spooks a buffalo, which gores Randy and others, and the address they seek turns out to be outdated. A party at a new house yields a possible lead, but the boy who might know the address does not actually know where Jeff lives now.
As the night unfolds, Miller and Casey uncover a troubling side of Jeff’s past: a gun in his possession and a history of having been arrested for attempted murder, leading many to label him a nutcase. The situation deteriorates when two stoned students at the party undress Jeff and glue a teddy bear to his penis. After the party, Jeff staggers into the street in this state and is arrested. Casey and Miller rush to the police station, only to learn he’s been moved to a mental hospital.
A trap set by the Latina students awaits them as they search for Jeff’s location; they are humiliated and pummeled, forced to walk campus in nothing but socks covering their penises to obtain new clothes, with Casey growing increasingly bitter at Miller for his role in the fiasco.
Inside the mental health facility, Casey and Miller want to bring Jeff home, but the hospital refuses. His file reveals a history of suicide attempts and a misfired gun during an alleged incident of attempted murder, prompting the desperate escape they devise: they smuggle him out by throwing him from the third floor, unsure if they’ve just killed him again—yet he remains uninjured. Awake and defiant, Jeff steals the car they were about to abandon, and they flee to the hospital file to discover his real address.
At last, the trio helps Jeff prepare for the medical interview. They remove the teddy bear and, in a crude moment, the prank leads to Jeff being momentarily exposed, yet they manage to get him dressed and presentable. Jeff opens up about the stress that pushed him to the edge, insisting he is not suicidal. Randy arrives at Jeff’s home intent on wrecking the room, but his father intervenes and defends Jeff. With Miller’s encouragement, Jeff asserts his own truth to his father, who initially resists until Miller steps in; Randy respects Jeff for standing up to his father, and the two reconcile.
Meanwhile, Miller’s future begins to look brighter. Though his grades had suffered from a lack of focus, he experiences a turning point and resolves to pursue higher education seriously. The night before Jeff’s interview, Miller slips away to a music festival with Casey, Nicole (who is Casey’s girlfriend now), and Jeff. The wild night culminates when Miller arrives at the professor’s door with a broken leg and flaming red hair, only to discover that the odd man he has been dancing with all night is the professor himself.
