Eric (Jason Sudeikis), a thirtysomething man-child, is defacto leader of his group of lifelong friends: McCrudden (Tyler Labine), an unemployed slacker; Alison (Lake Bell), a needy therapist stuck in a bad relationship; Adam (Nick Kroll), an uptight, nerdy office drone; Duquez (Martin Starr), a struggling musician; his free spirited girlfriend Willow (Angela Sarafyan); the virginal, insecure Laura (Lindsey Sloane); and Sue (Michelle Borth), who has a lifelong crush on Eric. There's also Glenn (Will Forte) and Kate (Lucy Punch), newlyweds with a baby.
The group hosts wild themed parties at Eric's family's summer home every holiday, until his dad decides to sell the place. As a farewell bash, Eric decides to host an orgy with all his closest friends, even though he unknowingly starts falling hard for his realtor, Kelly (Leslie Bibb). One by one, everyone agrees to the idea for different reasons.
At the orgy, everyone is so uncomfortable they start arguing, and Eric leaves to go profess his love for Kelly. He finds her on a date, however, and changes his mind. The orgy goes ahead, not including Glenn and Kate, who weren't invited, show up, but decide not to go in the house and instead end up having sex in their car. Everyone hooks up with everyone, and in the end: