AThe film actually follows the novel fairly closely in terms of structure. However, the film is significantly condensed as well as some other changes that are made.- In the book, Lisa is 14, Jenny is 31. In the film, their ages aren't given but Rose McGowan was 25 and Joanna Going was 35 at the time of the movie's release. Making both characters older than in the book.- Sheriff Bryce Hammond is described in the book as being 39, but having a relatively youthful appearance. Ben Affleck was only 27 at the time the movie was released.- Deputy Stu Wargle is very different in the film. In the movie, he is well-built, clean-cut but still has a slightly anti-social, obnoxious demeanor. However in the novel he is described as being overweight, a slob and insufferable. He also makes several disturbing comments about the 14 year old Lisa. He is killed in a nearly identical way in the film and the book. Only in the film, he is killed after a shoot-out with the giant moth creature inside a building. In the book he is killed in the street while the group was heading towards the inn.- Deputies Tal Whitmann, Gordy Brogan, Frank Autry and Jake Johnson are all excluded from the film. Instead replaced by Deputy Steve Shanning who is killed off fairly quickly.- Finding the bodies of Deputy Paul Hendersen inside the Sheriff's station, and the fact that he had fired off three rounds and appeared to hit his target and finding the body of Jenny's houskeeper are in the film as well as the book. However in the book they come across more bodies and do more searching as well.- The search of the Candleglow Inn is relatively similar. They also find the words "Timothy Flight The Ancient Enemy" written on a mirror and they later come across the severed hand with the lipstick that wrote it.- The sisters find the severed hands on the rolling pin and the severed heads in the bakery oven as well.- Timothy Flyte is relatively the same in the book and film. Except the Government brings him in as part of the HAZMAT team as a consultant in the film. In the book, an over-eager publicist brings him into the neighboring town in order to capitalize on the publicity and he volunteers to come into the town. In the book he is killed, in the movie he lives.- Dr. Sara Yamaguchi plays a much bigger role in the novel. She is the one who comes up with the idea of how to infect the creature after all the other scientists are wiped out. In the film, she is simply killed off and Flyte comes up with the idea on how to infect the creature.- General Copperfield's first name is Galen in the book and Leland in the film. In the book he simply vanishes along with all the other science team and soldiers. In the film, all the soldiers and scientists are systematically attacked and wiped out. The group witness Copperfield's death.- The sub-plot with escaped murderer Kale is omitted from the film.- The book ends with the creature having been infected and effectively destroyed. Tal, Jenny, Bryce and Lisa survive, Jenny and Bryce get married and the book ends on a happy note. In the film, they believe they have destroyed the creature however the end scene shows Stu Wargle sitting in a bar, hitting on a woman. Implying not the entirety of the creature was dispatched.
AIn the film, Bryce figures that the people in town that were killed by the creature felt that it was in fact Satan that was killing them and so the creature took on that role because that's what the people perceived it as. However, Flyte, Hammond, Jenny and Lisa all figure it's just some primeval creature that enjoyed playing the role of Satan in order to terrify its human prey. In the book, this idea eventually comes to pass but initially, the survivors are convinced they are dealing with a demon because they all got the same feeling of the presence of "pure evil". Eventually Flyte explains that he believes that the creature is Satan. Not the one from the bible however, but the creature that inspired the one in the bible. As every religion and culture around the world all collectively have their own interpretations of evil beings, demons, Satan, etc...Flyte believes that these are all people who have come into contact with "The Ancient Enemy" and lived to tell the story.
