A cross between “Dexter” and “Encyclopedia Brown,” “I Am Not a Serial Killer” follows John Wayne Cleaver, a 16-year-old Midwesterner being treated for sociopathic tendencies who is trying to resist his worst urges. Maybe John shouldn’t help out so much in the family business. His mother and aunt run a mortuary, and he’s really into prepping the corpses. He may not be a serial killer, but he sure likes studying them.

John (Max Records) perks up when his little community hosts one grisly murder, then another, and he sets out to solve the case. Whether fending off a bully, chatting with his therapist or living by the rules he’s set for himself to avoid his darkest impulses, John confounds his mother (Laura Fraser) but has a good relationship with a neighbor, Mr. Crowley (Christopher Lloyd). Incapable of emotional connections, John acts as if he has them.

Early in the movie, an adaptation of Dan Wells’s young-adult novel of the same name, the director Billy O’Brien nicely balances the tedium of small-town life — the film was shot in northern Minnesota — with an unnervingly creepy vibe. Unfortunately, the plot goes off the rails in the second half, as horror needlessly lurches into the supernatural.

Until then, though, Mr. Records (the child actor in “Where the Wild Things Are”) is nimble and unsentimental in playing a character who is playing at normal, supported by a solid cast in a well-filmed indie that doesn’t let its low budget get in the way of some true chills.