After a party, four teens are in a hit-and-run accident that results in a young boy's death. Unable to deal with the consequences, they leave the body behind and make an anonymous phone call to the police, tipping them off. The group makes a secret pact to bury the memory of that night and never speak of it again, but when one of the girls receives a note that reads "I know what you did last summer," their dark lie is unearthed. With twists and turns at every corner, they'll have to fight to stay steps ahead of a killer determined to make them pay.