What is the main conflict in 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.