朱莉(詹妮弗•洛夫•休伊特 Jennifer Love Hewitt )和其他三个中学生在毕业之际来到一个美丽的海滨城市, 开始了一次狂欢式的度假。怎料乐极生悲,四人在黑夜的公路上飚车撞死了一个路人。慌乱中他们决定把尸体抛入大海,并约定对此事守口如瓶。一个快乐的旅程以阴霾结束。
本以为一切都成为秘密。朱莉开始了她全新的大学生活。但是一封来信却打破了她的平静。里面赫然写着“我知道你去年夏天干了什么”,朱莉惊恐万分。果然,恐怖异样的事件开始发生在几个年轻人身上,他们推测凶手是谁,猜疑纷纷,然而血腥的结局早已在等待着他们……

I Know What You Did Last Summer is a 1997 American slasher film based on the 1973 novel of the same name by Lois Duncan. The film changes many aspects of the book, which was not a slasher novel. The film also draws inspiration from the urban legend known as The Hook.

The film stars Jennifer Love Hewitt, Sarah Michelle Gellar, Ryan Phillippe and Freddie Prinze Jr., with Anne Heche and Bridgette Wilson appearing in supporting roles. I Know What You Did Last Summer centers on four friends who are being stalked by a killer, one year after covering up a car accident in which they were involved. The film was directed by Jim Gillespie, from a screenplay written by Kevin Williamson, writer of Scream.

I Know What You Did Last Summer received mixed reviews from critics, but was highly commercially successful, grossing over $125 million at the box office. It was also nominated for and won multiple awards. As a result the film has been parodied and referenced in popular culture.

The film was followed by two sequels, I Still Know What You Did Last Summer (1998) and the straight-to-DVD release I'll Always Know What You Did Last Summer (2006). Though the former film sees a continuation of the plotline established in its predecessor, the latter film establishes a new plotline and does not star any cast members from the previous two installments.