When four friends accidentally hit and kill a man on a road at night, they start to panic and decide to dump the body into the sea. A year later, they all try to settle down again, but one of the friends receives a note in the post, with the words ’I know what you did last summer’. As each of the friends gains their own reminder, they finally accept the one thing they feared the most; someone knows what happened that night, and now they’re out for revenge.
