A group of teenagers is terrorized in a small Colorado town in this latest installment of the I Know What You Did Last Summer series. When a July 4th prank based on a frightening legend results in the accidental death of one of their best friends, the teens swear themselves to secrecy and to not tell a single living soul about their involvement. Their friendship is tested, however, as they drift further and further apart from each other until the following Independence Day, when they receive threatening messages suggesting someone else might also know what truly happened that fateful summer evening. Will they be able to stop the horrible legend from coming to life or be killed off one by one by the mysterious menace with the hook?