When five friends accidentally cause a fatal car crash, they decide to cover it up and form a pact of secrecy rather than face the consequences. A year later, their past comes back to haunt them, forcing them to confront a terrible truth: someone knows what they did last summer… and is bent on revenge. When each of them is hunted by a killer, they discover it has happened before, and they turn to two survivors of the legendary 1997 Southport massacre for help.