After a night of drunken partying, Tree Gelbman wakes up on her birthday in the dorm room of classmate Carter Davis. She dismisses him, returning to her room. Her sorority housemate Lori Spengler gives her a cupcake, which she throws away. Tree meets with her married professor, Gregory Butler, with whom she is having an affair. That night, on her way to a party, Tree is lured into a tunnel and murdered by a figure wearing a mask. She immediately wakes up back in Carter’s bed and is unnerved to find the previous day’s events repeating themselves. Baffled, she relives the day, this time avoiding the tunnel and reaching the party.