Detective Marvin Sludge, a former Special Services operative, lives a simple life. But he's the best detective in his department, the one always assigned to impossible cases and interrogations. With virtually no family left alive, he feels religion is for the weak and the soon-to-be-purged by natural selection—the ones who can't take the rigors of life.

Sludge, who suffers from PTSD, catches a curious case. A young man, a senator's son, has been shot, and experts find twenty-two shell casings at the scene. That evidence points toward the makings of a serial killer intent on murdering one person a week for the next twenty-one weeks. As the bodies continue to pile up, Sludge and his partner search for a pattern and the killer.

Soon the case requires him to attend a victim's church, starting him on his path to faith. Along the way, he addresses greater issues such as the meaning of life and who is really in charge of events.