The book focuses on the dual threats of the conflict between John and his darker side, which he calls "Mr. Monster", as well as the emergence of a second serial killer in Clayton County.

[5] He has also commented that writing the sequels to Serial Killer "really helped me grow as a writer, by forcing me to dig deeper into the character and find new ways to challenge him and myself.

"[7] This protagonist calls the darker part of his personality "Mr. Monster",[1] which was one of the aliases employed by serial killer David Berkowitz, also known as the "Son of Sam.

"[8] In the aftermath of the Clayton Killer, John Wayne Cleaver struggles to balance his desire to do and be good with his darker side, which he calls "Mr. Monster" and which he previously let loose in order to save the town.

His mom is now aware of his rules and helps to enforce them, but refuses to confront the reality that the Clayton Killer, posing as Mr. Crowley, was actually a demon.

John frequently meets with an FBI investigator, Agent Forman, but is careful not to reveal any information about the supernatural activity he witnessed or the fact that he himself killed Crowley.

A Savannah Morning News review complimented John Cleaver's characterization as "a nifty balancing act for Wells to have pulled off".

[10] Alternative Magazine also commended Wells's continuation of the storyline, saying that Mr. Monster "immediately addresses any faults with its predecessor's ending" while keeping the "strong aspects of the original story".

[11] Kirkus Reviews noted that "John's realistic familial relationships and friendships offer a counterbalance to the bloody, fantastical elements of the tale" and recommended the novel for "fans of genre mash-ups".

[13] Publishers Weekly wrote that the book "stands out with taut, sharp writing, strong plotting, vivid angst, and a compelling portrayal of a disturbed man's struggles for self-control".