Everything you need to understand or teach I Know What You Did Last Summer by Lois Duncan.
The mysterious clues come in a year after the accident. Julie gets a nondescript letter in the mail with only seven words on it that says, "I know what you did last summer." Then Helen finds a picture of a boy on a bike ripped from a magazine advertisement of some sort, taped to her apartment door. A short while later, Ray gets a similarly nondescript envelope in the mail that contains only a newspaper article about the accident. Finally, Barry gets a phone call to meet someone at the football field amid the firework celebration and gets shot.
After each contact from the unknown person, Julie, Helen, Ray, and Barry talk to each other about who could be leaving these messages and what they all mean. Eventually, the details of what happened last summer come out. Barry was driving recklessly on a winding road with Helen next to... View more of the I Know What You Did Last Summer Summary