Why was the author of 'I Know What You Did Last Summer' horrified?

I Know What You Did Last Summer was adapted from a film in 1997. But what made the book’s author, Lois Duncan, “horrified” was the changes to the film’s script without her knowledge.

Clark Collis, in his upcoming non-fiction book, Screaming and Conjuring: The Resurrection and Unstoppable Rise of the Modern Horror Movie, sheds light on this, revealing the late author only came to know the changes when she watched the horror flick.

It was screenwriter Kevin Williamson who rewrote and added new parts, including creating the villain, Fisherman. 

In Clark’s book, he explains that he comes "from a fishing community in North Carolina" and uses his background to come up with new ideas as he recalls his conversations with his father.

"I went to my dad, and he walked me around the boat, and he showed me the A-frame, and how someone would be jerked up to the top," Kevin shares. "Then I wrote it, and he went, ‘Kevin, that would never happen.’ I said, ‘Yes, but it’s in the movie, Dad.'"

"We added Johnny Galecki’s death scene on camera, and we changed the ending," he says as his creative choice made the film a cult-classic.

I Know What You Did Last Summer is running in cinemas.