Aside from the characters names and the teens hitting someone with their car, the plot is almost completely different from the original novel. In the novel they did not hit a fisherman but a young boy who was the brother of one of Helen's new friends. In addition, no one dies in the book. Barry is shot with a gun but survives and Julie comes to a close encounter and was almost choked by Collie, the boys brother, but Ray hits him with a club.
Despite being part of the main cast and appearing in many key scenes together, the characters Helen (Sarah Michelle Gellar) and Ray (Freddie Prinze Jr.) only speak to each other twice (Ray - "How do you know that?" Helen - "Missy, said there was a friend named Billy Blue)" (at around 1h 2 mins) and (Ray - "No, it's not, it's true" Helen "Yeah, I don't think so, Ray") (at around 10 mins). In real life, the two later fall in love and marry.
The original trailer for the movie described Kevin Williamson and the movie as "from the creator of Scream (1996)". Miramax, owners of the "Scream" franchise successfully sued Columbia Pictures for "false advertising" and the phrase was removed.
The set relocated from North Carolina to California for the scene where the four teenagers run over the man. Producer Erik Feig said that North Carolina was the flattest state and they needed a more 'curvy' and 'dangerous looking' road.
Jennifer Love Hewitt had just appeared along former Scream Queen Jamie Lee Curtis in House Arrest (1997) prior to filming this movie and was surprised to see she was also filming a movie in North Carolina at the same time. Jennifer said Jamie came over to the soundstage to wish her luck on her first horror film and would come over every day after that to give her a hug.
The scene where Helen (Sarah Michelle Gellar) escapes from the cop car mirrors a similar scene in Scream 2 (1997) with Sidney and Hallie. Sarah Michelle Gellar plays the sorority girl Cici in said film.
The trivia items below may give away important plot points.
The film originally had a different ending, where Julie James is chatting with Ray online, she gets the pool party invitation, and then another person starts a chat with her typing in, "I still know." Then the killer jumps out on her. This ending was used as a teaser trailer for the sequel.
The last thing that Max says to Barry is that he is going to turn him in to the police. It is later established that the killer had followed the four leads to the fishing pier and had taken pictures. This implies that he had witnessed the scene where Barry threatens Max and finally learned that Max was present when the car accident happened. This provides a motive about the murder of Max, since the police would have taken Barry under custody for the assault against Max or at least would have watched him. Further investigation about the involvement of the five teens in the fatal night with possible links to the David Egan drowning case would have led to even more interrogations and undoubtedly the killer's plans would have been foiled since he had only a couple of days before the 4th of July. This explains why Max was dispatched right afterwards while the killer continued to stalk the other 4 leads knowing that they could not resort to the police.
Max's Murder was added in re-shoots. It was decided that the killer, who remained mostly in shadows for the first half of the film, worked on a suspense level, but never provided a tangible threat to the main characters. The murder was then filmed to show the audience that, indeed, this character was a deadly threat to the four leads.
In the book all the characters live. And the back story to the what happened in the car accident is explained in a lot more detail. The movie basically only took the title to the book because in the end the teens come clean to the police in the book.
The movie uses only a few plot points from the source material. The novel has a pedatrian killed by a car and the protagonists are stalked by an unknown killer the following summer. Almost all of the other elements are ignored to fit the unstoppable killer slasher film mold. The movie also makes the protagonists look more sympathetic by having them discover at the end that the pedestrian hadn't been killed.