- "I am death...plain and simple."
In the novella, Cabal, Decker is Boone's psychiatrist. He is first encountered when he meets with Boone and discusses his concerns regarding police evidence that points to Boone as a vicious serial killer.
Decker claims that he has audio recordings of Boone vividly describing the murders while under hypnosis. He gives Boone some pills and tells him they have to solve the issue or he'll turn Boone over to the police.
He later finds Boone in the abandoned town of Midian and admits to killing the people Boone thought he was guilty of murdering. He explains that he likes it and saw Boone as a way of getting away with it.
His intentions are to frame Boone and move to a town far away so that he can continue killing without raising suspicion. His drive to kill is fueled by his schizophrenia and projected character of The Mask or Ol' Button Face. This mask speaks to him, whether or not he is wearing it, and commands him to kill. They both receive intense sexual pleasure from killing families and children.
After Boone escapes from the morgue, Decker stalks Lori to Shere Neck, with the intention of finding Boone and covering his tracks. He deceives a newly made friend of Lori, Sheryl Ann, to be a banker named Curtis.
Using the guise of Curtis, Decker lures Sheryl Ann and Lori into an abandoned restaurant, where he slits Sheryl Ann's throat and reveals himself to Lori.
Lori escapes and rushes to the Necropolis outside of Midian where the Nightbreed live. Decker chases her in hot pursuit but is interrupted by Boone and Narcisse, who threaten him and attempt to take his life. He narrowly escapes and is not seen until outside the motel, where Boone is arrested for killing the entire population of a roadside motel (approximately 30 people). He led the Shere Neck police force on a lead regarding the pursuit of Boone, hiding the fact that he killed all of the people in the motel.
Using his credit for leading Eigerman and his force to the arrest of Boone, he convinces Eigerman to invade Midian and eradicate the monsters that live underneath the ground, due to their abominable nature.
During the attack on Midian, The Mask calls to Decker and he dons it once more, with intentions set on killing Lori and Boone, covering his tracks once and for all. He is interrupted in pursuit of Lori by Narcisse, whom he decapitates with his blade. Midian begins to collapse around him during his chase and he finally finds Boone, who turns into his monstrous form and fights Decker, killing him with his own blade.
- Gift shop owner
- Motel receptionist
- Motel employee
- Motel guests (unclear as to how many)
- Ten families (mentioned in a session with Boone; it is unclear how many members were in each family)
Due to the unclear nature of how many people Decker has killed in each scene, it can only be safe to presume that the body count lies somewhere in vein of the proximity of victims in the novel, which is somewhere around 60.