"Snowfall" is the story of Caitlin Bennett, a successful writer of murder mysteries, who becomes the target of a serial killer herself. The heiress to a large fortune, Caitlin has always been comfortable, as well as having made a name for herself as a writer. However, at the beginning of the novel, she has begun to receive threatening letters from an unknown assailant. At first, she is quiet about these letters, until Caitlin is pushed in front of a truck and her editor, Aaron, reveals that the publishing house has also been getting them. As she recovers, Aaron has his brother, Mac, a former police officer, come to protect Caitlin even though the two have never gotten along well.

Meanwhile, the police work on solving not only the mystery of Caitlin's enemy, but also the murders of several women in New York City. They cannot seem to piece together the identity of the attacker. At the same time, a man called "Buddy" is the one who has been murdering them because they resemble Caitlin and he hates her so much.

Frustrated by her inability to do anything, and thinking that she will catch the attacker, Caitlin makes an announcement publicly that the man pursuing her is a coward. However, she underestimates Buddy, who sends a bomb to Aaron's office, seriously injuring Aaron. Beginning to fall in love, Caitlin and Mac go to visit Aaron in the hospital, where Caitlin befriends a little girl who has been traumatized by her mother's death. Caitlin and Mac are still trying to solve the mystery, and begin to connect the murders to Caitlin when they visit the police precinct and Caitlin faints, realizing that all of the dead women resemble her. They then make the link to Caitlin's father, and try to talk to his former secretary; however, she is brutally murdered before they can get to her. They then go to talk to Caitlin's father's lawyer, who reveals that her father had sent money every month to a woman in Toledo.

With some research, Mac discovers that this woman had had a child by Caitlin's father, and refused money from him, though he sent it regularly each month. However, he also discovers that the child is Neil, one of the police officers on Caitlin's case - also known as "Buddy." He goes to get Caitlin only to find that she has unknowingly gone with Buddy to his cabin. With other members of the police force, Mac goes to save Caitlin, though he has to kill Neil in the process.