“Women are the real architects of society.”

As millennial teens, my friends and I all loved I Know What You Did Last Summer. It was a staple at sleepovers, with entire scenes viewed through our fingers as each character met their bloody fate. The film was part of a wave of teen slashers in the mid-to-late-90s. Although the film is admittedly violent, it wasn’t something any of us would think about too seriously, since the issue of teen murder didn’t hit close to home for us. Unfortunately, the same doesn’t hold true for the book’s author. 

Hollywood making major changes when adapting novels is certainly nothing new. The stale declaration that “the book was better,” albeit annoying, is frequently true. When taking the tragic details of the author’s real life into consideration, however, I Know What You Did Last Summer may be one of the most egregious examples. 

In 1989, eight years before the film, Duncan’s 18-year-old daughter Kaitlin Arquette was tragically murdered while on her way home from a friend’s house. Frustrated by the lack of progress in the police investigation, Duncan began her own search for her daughter’s killer. She wrote about the case and investigation in Who Killed My Daughter?, published in 1992. The case remained unsolved for decades, fueling the author’s relentless pursuit for justice. As Duncan herself stated, “My dream is to write a sequel to Who Killed My Daughter? to give our family’s true-life horror story closure. Of course, Kait’s case must be solved.”

 The decision to change I Know What You Did Last Summer into a straightforward horror film inspired by the 1980s slasher genre was influenced by the success of the 1996 smash hit Scream, although Kevin Williamson, the screenwriter of both films, reportedly did not know about Duncan’s personal tragedy. 

Unlike the film, Lois Duncan’s original story published in 1973 did not contain any of the slasher elements that made the adaptation a cult classic. Instead, the story centered around the main characters coming to terms with their decision to flee the scene after hitting a young boy on a bicycle on a fateful rainy night. The teens are haunted by the repercussions of their own actions, not by a hook-wielding maniac.

Duncan reportedly urged family and friends not to see the film, stating that the adaptation was “sick.” She spoke out publicly against the film saying “The gore was beyond belief. I write suspense and scary stuff, but I have never written gore in my entire life. I have never sensationalized violence. It’s always been a vehicle to show the pain that violence can cause. There’s so little connected to my book that I don’t know why they ever wanted it.” 

Despite her anger at the changes, Duncan did concede that the film sparked a renewed interest in her work, stating that she was “happy with the fact that the book had been made into a movie, because that made all my backlist suddenly very popular. It was like getting a rebirth, but in a very strange way.”

Justice for Kaitlin finally came, although the author did not live to see it. The case was solved when Kaitlin’s killer confessed in 2021, five years after Lois Duncan’s death. While Duncan’s real-life horror story has written its final chapter, the fiction she abhorred lives on. I Know What You Did Last Summer received yet another sequel in 2025, securing the legacy of the franchise as a chilling form of entertainment born from a story whose author knew the true cost of violence.