Todd (Labine) wants everything to be just perfect at the family cottage where he plans to propose to Cammie (Akerman). But things go awry with the arrival of Todd's slacker brother Salinger (Petronijevic) and his free-spirited girlfriend Masha (Punch). When Todd accidentally dispatches his irksome sibling with an axe, Cammie is determined not to let murder stand in the way of their happiness.

The movie will shift its focus on Erik Stifler, the cousin of Matt and Steve, a youngster who is nothing like his wild relations. Peer pressure starts to turn him to live up to the legacy of the other Stiflers when he attends the Naked Mile, a naked run across the college campus. Things get worse when he finds that his cousin Dwight is the life of the party down at the campus.