31 Mar Book Review: I Know What You Did Last Summer by Lois Duncan

Lois Duncan is a name that looms large in the world of young adult suspense fiction. Long before psychological thrillers became a staple of the YA genre, she was writing stories that tapped into the universal fears of teenagers—secrets, guilt, and the realization that the past always catches up with you. I Know What You Did Last Summer is one of her most famous works, a tightly woven tale of paranoia, consequences, and the lengths people will go to in order to keep the truth buried. It is a novel about how one mistake can spiral into something much worse and how fear can turn even the closest of friends against each other.

What’s it about?

It all starts with a single, terrible decision. One summer night, four teenagers—Julie, Ray, Barry, and Helen—are driving on a deserted road when they accidentally hit a stranger. Instead of reporting the accident, they make a pact to keep it a secret. They move the body, erase any evidence, and promise never to speak of it again. Then, they go their separate ways, trying to forget that anything ever happened.

But secrets have a way of refusing to stay buried.

A year later, Julie is trying to move on. She has transformed herself from a carefree high school girl into a serious college student, hoping to distance herself from the past. But one day, she receives an anonymous letter with a terrifying message: I know what you did last summer.

Julie is not the only one being targeted. Helen, who has left school behind to pursue a career as a television personality, begins to sense that someone is watching her. Barry, ever the arrogant and reckless one of the group, laughs off the idea of someone coming after them—until he finds himself face-to-face with a threat he can no longer ignore. Ray, who has spent the past year drifting, trying to escape his own guilt, realizes too late that there is no running from what they did.

At first, they try to convince themselves it is just a cruel prank. But when Barry is attacked, they understand that this is not a joke. Someone knows what they did, and whoever it is wants revenge. As the threats escalate, they begin to turn on each other, unsure of who they can trust. Could it be a witness from that night? A family member of the victim? Or is it one of them, cracking under the pressure and trying to scare the others into confessing?

As Julie and the others scramble to uncover the identity of their tormentor, they realize that their pact—the thing that was supposed to keep them safe—has become their greatest vulnerability. And the deeper they dig, the closer they come to the terrifying truth: someone out there does not just want them to suffer. Someone wants them dead.

What This Chick Thinks

A suspenseful story that taps into real fears

One of the reasons I Know What You Did Last Summer works so well is because it is not just about a mystery—it is about guilt, consequences, and the fear of being found out. Unlike supernatural horror, this story is frightening because it feels possible. It is about the ways in which a single bad decision can ripple out, affecting people in ways you never anticipated.

Complex characters with believable flaws

Julie, Ray, Barry, and Helen are not perfect protagonists. They are selfish, impulsive, and often frustrating. But that is what makes them feel real. They did something awful, and while they regret it, their first instinct is not to do the right thing—it is to protect themselves. Watching them struggle with their guilt, their paranoia, and their growing sense of dread is what makes the novel so gripping.

A slow build that keeps you on edge

Unlike the more action-heavy horror films that this book inspired, the novel takes its time setting up the tension. It does not throw you into a bloodbath from the first page. Instead, it builds the suspense gradually, letting the sense of unease creep in until you are just as paranoid as the characters.

A different ending from the movie

If you are coming to this book after watching the 1997 film adaptation, be prepared for some big differences. The novel is much less focused on slasher-style horror and more on psychological suspense. The ending is not nearly as explosive or over-the-top, but it does leave a lasting impression. It is more about the characters facing the weight of their choices than about a masked killer jumping out with a hook.

Final Thoughts

I Know What You Did Last Summer is a classic for a reason. It is a story that plays on primal fears—the fear of being watched, the fear of being punished, and the fear of a past mistake coming back to destroy your life. It is not just a mystery, but a morality tale about how guilt festers and how secrets never truly stay buried.

While it may not be as fast-paced or terrifying as modern thrillers, it is still an engrossing read that holds up decades after its original publication. If you enjoy suspenseful stories that focus more on tension and character than gore, this one is definitely worth reading.

Rating: 8/10

Try it if you like

• Ten by Gretchen McNeil – A modern YA thriller about a group of teenagers trapped on an island, being picked off one by one for their past mistakes.
• I Am the Cheese by Robert Cormier – A psychological thriller that plays with memory, secrets, and paranoia.
• The Cheerleader by Caroline B. Cooney – Another classic YA thriller about a seemingly perfect girl whose life begins to unravel when she gets caught up in something sinister.