However, a year later, they start receiving mysterious messages and gifts that suggest someone knows about their dark secret. As the threats escalate, the friends begin to suspect that someone is trying to exact revenge for their actions.

The story revolves around four high school friends - Julie, Ray, Helen, and Max - who are involved in a hit-and-run accident on a summer evening. They panic and decide to keep the incident a secret, disposing of the body and vowing never to speak of it again.

Lois Duncan's "I Know What You Did Last Summer" is a gripping and intense novel that explores themes of guilt, paranoia, and the consequences of one's actions.

The novel builds up to a thrilling climax as Julie, the protagonist, tries to uncover the identity of the person who knows their secret and is determined to expose them.