Before Jennifer Love Hewitt and her castmates ever felt the sharp end of an ice hook, I Know What You Did Last Summer was a novel by Lois Duncan. The famed young-adult author proposed a dilemma like few others when she pursued an idea of dual identities and a curiosity about hit-and-runs. This seminal 1973 book follows four teens who fail to do the right thing one fateful summer. And after a year of waiting and trying to forget that awful night, their past finally catches up with them.

Unlike in Jim Gillespie’s 1997 film, Duncan’s story goes straight to the aftermath; it begins almost a year after the hit-and-run, shortly before Memorial Day. There are no prefacing displays of happier times to offset the new normal for the main characters. For Julie James, good news about college coincides with an ominous letter. Helen Rivers’ coveted job of a glorified weather girl and Barry Cox’s man-on-campus status are also eventually spoiled by menacing reminders of last summer. Julie’s ex-boyfriend Ray Bronson has returned from California a different man, but no amount of soul searching on a boat can undo what he and the others did.

The two Julies are only vaguely similar. The book version, still a senior in high school, ditches cheerleading to focus on getting into a good college and out of a town tarnished by one horrible memory. Since they made the pact, Julie is adamant about cutting off ties with the group; she only contacts Helen and Barry for answers about the note she received. The threat diminished what little of Julie’s spirit was left, leaving her positively defeated even after being accepted into college. In contrast, the film’s Julie is less passive and more willing to fight for her life following the discovery of a dead body in her car trunk.

Duncan’s Ray Bronson is thoughtful and more well-rounded, when compared to his on-screen parallel. Being smart is evidently not good enough for Ray’s father in the book; the Bronson patriarch is a former athlete who wants Ray to follow in his footsteps. Being of small stature and less inclined toward sports, though, Ray feels like a disappointment. The bright spot in his life was once his relationships with Barry and Julie; Ray could vicariously feel loved through Barry, the son Ray’s father wished he had, and with Julie, he cared for her deeply. Still does upon his return to town after running away to find himself and to make sense of everything. This Ray and Freddie Prinze, Jr.’s incarnation have at least one thing in common; the villain refrained from killing Ray because he knew hurting Julie instead would amount to a kind of pain far more unbearable.

Julie is without question the central character in the I Know What You Did Last Summer film; the audience relates to her as she tries to convince her friends to report the accident. But if only one character in the adaptation gathered an excess of pity, it was Sarah Michelle Gellar’s Helen Shivers. The girl with big dreams is done in by reality first, then a merciless killer. Her lengthy chase across town, first through a department store, and later an alleyway, is earmarked as one of the best (and saddest) in the whole slasher subgenre. It was Gellar’s Helen who truly voiced the consuming yet unspoken sorrow among the four characters. With three lines in a choice scene with Julie — “What happened between us? We used to be best friends. I miss you.” — Helen both broke and stole the audience’s heart.

The book, on the other hand, gives more of the spotlight to Julie’s former confidant, Helen Rivers. As self-absorbed as she is, Helen is determined to live. She stops at nothing to escape her unhappy home situation; she wants more than the impoverished and unfulfilling life her parents have. And as seen in the story’s most kinetic scene, Helen also refuses to let her stalker take her down. If Miss Rivers has one weakness, though, it is Barry Cox. Helen gives her fickle boyfriend every benefit of the doubt until she has no choice but to see his true colors. Her wake-up call comes at the worst moment possible; the antagonist is making good on his threats, starting with Helen. And before Helen demonstrates her vast will to survive, she realizes Barry does not love her. His betrayal and dishonesty has only put all of them in direct harm.

Neither representation of Barry is all that becoming. In the book, he is almost unremittingly selfish. This Barry originally dates Helen because her background bothers his snooty mother, and he only stays with Miss Rivers after the accident because she sided with him. That obligation wanes soon enough, and once in college, Barry dates other women behind Helen’s back. There is then an apparent sense of self-loathing in Barry, particularly after he is shot. Him being the only character to be physically harmed has to do with his being behind the wheel that night. Better late than never, Barry has a change of heart before someone else gets hurt. At long last, he ends the pact preventing everyone, including himself, from moving on with their lives.

Something overlooked in the original I Know What You Did Last Summer is the relevance of its time period and how it relates to the main plot. The book first came out in the fall of ‘73 right when the United States was in the middle of a major transition. The last U.S. combat troops had left South Vietnam earlier that year, and America’s part in the Vietnam War was finally coming to an end. The war was a part of the backdrop, but the author made sure to reflect these shaky times both directly and quietly. There is mention of campus unrest, and Barry’s near-fatal shooting is first thought to be the work of a random protester with a gun. On top of that, Julie’s new boyfriend Bud is a young veteran. His succinct response when asked about his experience in Vietnam? “War is hell.”

It might not have been intentional on her part, but Duncan having young people kill someone, then letting the trauma manifest is a usable metaphor for a soldier’s PTSD. At the time, I Know What You Did Last Summer was just one part of the media trying to address an issue on everyone’s mind as U.S. soldiers returned from serving overseas. Similarly, Julie and her friends took a human life, and they now feel haunted. Ray comes home with a tremendous amount of guilt; Julie is a shell of her former self since the accident. While their friends are the most affected by the coverup, Barry and Helen have rationalized killing someone because their welfare mattered more than some stranger. The book conveys a shrewd yet ponderous outlook on the necessity of war at a time when it was impossible not to think about such things. Meanwhile, screenwriter Kevin Williamson dropped the war aspect altogether in the film and gave everyone’s grief and trauma a more tangible form.

In Fangoria, issue 168, Williamson spoke highly of Duncan’s novel, but he also added, “No one really gets killed.” This led to him bringing I Know What You Did Last Summer straight into the ‘90s and up to code with modern horror. In addition, the producers asked Williamson to come up with a villain mythology “that would lend itself to a sequel.” As a result, the book’s stalker was turned into more of a traditional slasher villain in the film. The antagonist, now known as The Fisherman, was clearly made with Scream’s Ghostface in mind, although his obscured appearances are objectively more unnerving. Regarding the book’s low carnage, Williamson then included a modest body count. Needless to say, these new developments did not sit well with Duncan, who went on record to say she was “appalled” by the film’s slasher dressings. Something to keep in mind when evaluating  Duncan’s opinion is the fact that her daughter was murdered in 1989, and until five years after the author’s death, the case was unsolved for three decades.

Where else the text and the film significantly diverge is the hit-and-run victim’s identity. As grisly and mean as the big-screen I Know What You Did Last Summer adaptation comes across, it lacks the follow-through of the novel. In place of a bicycling boy in the wrong place at the wrong time, Williamson devised a whole new character for Julie and her friends to both run over and later do battle with. And contrary to the villain’s motive in Duncan’s story, The Fisherman is not avenging a loved one; he himself is a murderer prior to the car accident. This development entails an awfully convenient get-out-of-jail-free card at the end of the film.

The ‘97 adaptation has since gone on to overshadow its basis; some fans would go as far as to say it improved on the source material. A closer look at Duncan’s work, however, reveals a persuasively told thriller packed with emotion. And what the book lacks in overt thrills and murder it certainly makes up for in well-formed, complicated characters who all experience catharsis. To many people nowadays, the key version of I Know What You Did Last Summer is the film, but the novel, in many respects, better communicates this unique morality tale.

Editor’s Note: This article was originally published on July 6, 2022.