[1] It tells the story of teenage sociopath John Wayne Cleaver, now seventeen years old and the member of a team of FBI agents dedicated to hunting down a network of supernatural murderers known as "the Withered."

The Devil's Only Friend is the fourth book in the John Wayne Cleaver series, preceded by I Am Not a Serial Killer (2009), Mr. Monster (2010), and I Don't Want to Kill You (2011).

[3] Wells originally opposed continuing the series because he felt that "John's character arc concluded in what [he] thought was a very satisfying way.

[5] He wanted to "explore the demons more," particularly their past, and to "take John in a new direction: not to repeat his character arc from the first series, but to build on it and show him grappling with new emotional problems.

"[6] In addition to John, Wells "particularly enjoyed" writing the characters of Agent Potash and Elijah Sexton, who are introduced in the novel.

Their next target is Meshara, a demon in the body of a man named Elijah who consistently visits a patient with Alzheimer's.

John figures out that the Hunter has faked being a cannibal to throw them off the scent of who he really is: the king demon Rack, whose defining characteristic is his lack of a mouth and heart.

Herb Scribner for Deseret News praised the "imagery and ... vivid storytelling" present in The Devil's Only Friend, but disapproved of the amount of supporting characters and plot twists.

"[8] Marty Mulrooney for Alternative Magazine Online writes: "The only real downside of the book is that John’s reluctance to connect with the people around him can stop the reader doing so too.

[10] Craig Clark for Booklist also praised the prose, and added: "John's first-person narration is at once deeply disturbing and darkly humorous.