Newlyweds Alex (Lee Tergesen) and Alice (Melanie Lynskey) are hosting a New Year's Eve party for their closest friends at a remote cabin in the mountains. But when the other couples arrive in various states of discord, their hopes for a relaxing weekend are quickly thrown out the window. The tensions in the cabin are compounded when Alice's friends bring along a surprise guest, the very young and very beautiful Helena (Gillian Jacobs). As the New Year creeps closer and closer, Alex and Alice must keep the evening from spiraling out of control... and their own marriage from coming unglued.