Bestselling mystery writer Marty Stillwater was recording himself one day when he realized that he was saying "I need..." repeatedly. When he went back to see what he had been saying before he found out he had been saying "I need" for over 7 minutes. Marty was tense that whole day, when he put the kids to bed though he calmed down considerably and was finally consoled.

Meanwhile, the Killer was roaming the streets before his job, when he went into a bar and went with a prostitute to a motel and slept with her but soon after became angry because he felt dirty, and murdered her. Then proceeded back to his job. He kills his targets and goes to the hotel he is staying. That night, being restless, he leaves his itenary and goes towards Topeka. Suddenly, he starts saying:

"I need... to be... I need to be... I need to be..." As the suburbs and finally the dark prairie flash past on both sides, excitement builds steadily in him. He trembles on the brink of an insight that, he senses, will change his life. "I need to be... to be... I need to be someone." At once he understands the meaning of what he has said. By "to be someone," he does not mean what another man might intend to say with those same three words; he does not mean that he needs to be someone famous or rich or important. Just someone. Someone with a real name. Just an ordinary Joe, as they used to say in the movies of the forties.

—?Mr. Murder page 48-49

The Killer was attracted like a magnet by some force he didn't understand to the Stillwater residence. On his way he killed several people, an old couple for a set of clothes and a gas station clerk for food and to save money. When he breaks into the house he sees a picture of Marty and notices he looks exactly like him. He sees the pictures of the daughters Emily and Charlotte and Marty's wife Paige, he then decides he wants to be the father and husband. He goes to the computer to write a book, but since he can't he destroys the computer.

Marty was quite upset about his fugues (a break in one's memory) and so went to see a doctor. The doctor said it was just stress.

When Marty comes home he found things misplaced and his computer smashed. The Other than comes and Marty shoots him twice in the chest, but he gets away. Then they fight and the Other gets away. Marty's wife then comes home, and Marty sends them to their neighbour's house. Soon after, the police arrive. Cyrus Lowbock, the detective, interrogates Marty and doesn't believe him, so Marty sends him away.

The Killer was hurt so he needed food, so he went to McDonald's and ate enough for six. Then he went to get the women that he thought were his from who he thought was an impostor. He went to the neighbour's house and got the daughters, but as he was leaving Marty came out and the girls escaped to him. The Killer fled again.

Drew Oslett and Karl Clocker were going to where The Killer (whom they referred to as "Alfie") had killed two seniors and taken out his tracking device. When they arrived and saw he wasn't there they left and found a picture of Marty in a People magazine and saw he looked exactly like Alfie. They then went to see a contact that might help them find Alfie. After discussing they decided the Stillwaters had to be terminated to look like a murder/suicide and Alfie had to be brought in.

Meanwhile the Stillwaters fled to a cabin in Mammoth Lakes and set up to get attacked by The Other. Paige hid under a rock to ambush The Other, but impredictably he ran his car through the cabin. The Stillwaters then fled to an abandoned church. Here Marty is shot and Paige and the girls leave. As The Other comes Drew and Karl track him and enter. Drew kills The Other and is then killed by Karl who rescues the Stillwaters provides them with new identities, a new home and evidence to bring the company down. After a few months Marty mails the evidence to the authorities from an anonymous name thus ending the story.

Marty Stillwater - Marty is a mystery novelist. His wife is Paige and they have two daughters: Emily and Charlotte.

Paige Stillwater - Paige is Marty's wife and is a counselor.

Charlotte Stillwater - First daughter of Marty and Paige.

Emily Stillwater - Second daughter of Marty and Paige.

The Killer - A genetically engineered clone of Marty that is named Alfie. He was created by mistake. Has been trained in many forms of combat and is experienced in "real world" combat missions.

Drew Oslett - Alfie's handler. He is paired with Karl Clocker, whom he despises.

Karl Clocker - Karl is paired with Drew.

Cyrus Lowbock - Lowbock is a cynical detective who was in charge of the investigation of Marty's attack. He didn't believe the story Marty told him, which caused Marty and Paige to kick him out of the house.

Koontz sold the film rights to Mr. Murder to Savoy Pictures after the book's publication. The adaptation was initially scheduled to be a big budget theatrical feature in 1996 starring Bruce Willis as Marty Stillwater and to be directed by Uli Edel. However, this version never came into fruition.

With the feature film unable to get off the ground, the rights were sold to a different production company that developed the project as a miniseries on a much smaller budget. This adaptation was directed by Dick Lowry from a teleplay by Stephen Tolkin. The cast included Stephen Baldwin as Marty Stillwater, Julie Warner as Paige Stillwater, Thomas Haden Church as Drew Oslett Jr., and James Coburn as Drew Oslett, Sr., a character not in the book. It was broadcast in New Zealand on September 21, 1998, and was later broadcast in the United States on ABC on April 26 and April 29, 1999.^[4]