When five friends inadvertently cause a deadly car accident, they cover up their involvement and make a pact to keep it a secret rather than face the consequences. A year later, their past comes back to haunt them and they're forced to confront a horrifying truth: someone knows what they did last summer... and is hell-bent on revenge. As one by one the friends are stalked by a killer, they discover this has happened before, and they turn to two survivors of the legendary Southport Massacre of 1997 for help.