I Am Not a Serial Killer

15-year-old John Wayne Cleaver is a diagnosed sociopath who lives above a mortuary owned by his mother and her twin sister, Margaret. His parents named him after actor John Wayne, but he notices that he also shares the name with serial killer John Wayne Gacy. He is obsessed with serial killers, and has extensive knowledge of their behaviors. John himself exhibits a few of these characteristics, such as wetting the bed, fascination with fire, and abusing animals. He fears that he is "destined" to become a serial killer, so lives by a set of rules designed to keep his homicidal impulses in check and keep him "normal". He forces himself not to obsess over any one person, to sit with a boy named Max during lunch to maintain a sort of friendship, and to attend therapy sessions with a counselor, Dr. Neblin.
After a serial killer comes to Clayton County, North Dakota, John decides to throw all his rules aside in order to catch the culprit. As the victims' bodies come to his family's mortuary, John notices that there is a part missing from each: for one, it is a kidney, for another, an arm. His conversations with Dr. Neblin become focused solely on the killer. Soon, John discovers that his neighbor Mr. Crowley is the guilty party; John watches as he transforms into a demon who kills to replace his own failing body parts. In the following weeks, he watches Crowley kill another innocent man, two police officers, and his friend Max's dad. He begins to leave Crowley anonymous notes threatening to expose his true identity. John wonders why Crowley stays in Clayton, then discovers that it is because he truly loves his wife, Kay. John notes this paradox: Crowley is a demon who can love, and he himself is a human who cannot.
John makes the decision to use the demon's weakness against it by sneaking into the house one night while Crowley is gone, knocking Kay out and sending pictures to Crowley. Crowley takes the bait; he returns to the house as John is leaving. However, it is too late: he has killed again, and the body is in his passenger's seat. It is Dr. Neblin, John's counselor. John takes Neblin's body and hides in a shed, hoping that Crowley will grow too sick and die before he can replace his failing organs with Neblin's. John's mother arrives, looking for him in the night. As the demon heads towards her, John runs to her, and the two escape to the embalming room. The demon follows them, and John destroys it using a bladed trocar. In the aftermath of this event, he begins to make an effort both to get to know his mother and to come to know who Mr. Crowley used to be by visiting Kay.