It's near the end of the high school year, and seniors and best friends Seth (JONAH HILL) and Evan (MICHAEL CERA) have learned of a big party being thrown by Jules (EMMA STONE). Seth is enamored with her, but being a nerd like Evan -- who likes Becca (MARTHA MACLSAAC) -- and their friend Fogell (CHRISTOPHER MINTZ-PLASSE), who's smitten with Nicola (AVIVA), he doesn't stand a chance.
That is, unless he can ply her with liquor, a supposedly surefire but only rumored tactic the guys are willing to try. The problem is that none of them are old enough to buy booze, but with Fogell sporting a fake I.D. that states his name is McLovin, he decides to give it a try.
Just as he's about to succeed, a liquor store robber decks him, resulting in Officers Slater (BILL HADER) and Michaels (SETH ROGEN) arriving on the scene. A pair of goofballs, they end up taking Fogell on their nightly rounds, including stops at bar where they get liquored up.
At the same time, Seth and Evan hope to score liquor elsewhere, a quest that ends up getting more complicated than they ever imagined. With the night wearing on and fearing they might miss their chances with the respective girls of their lustful dreams, the three guys do what they can to make it to the party and get those young women drunk before it's too late.