The latest installment in the "I Know What You Did Last Summer" franchise focuses on a seemingly harmless Fourth of July prank that ends in the unexpected death of a friend of four teens from a small Colorado town who make a pact to keep the death a secret (despite one's desperate protest). Over the course of the following year, the four teens find their friendships all horribly strained and all but terminated completely from the trauma. Come the next Fourth of July, just before the town's annual carnival, the four teens all find themselves being victimized by a mysterious menace when they begin to receive intimidating calling cards indicating someone is aware of what happened before. The group suspect the cousin of the dead friend, only to discover they are very much on the wrong track. Can the friends survive and figure out the identity of their tormentor before they end up dead themselves?