J. D. Barker’s The Fourth Monkey operates within the established conventions of the serial killer thriller, a subgenre popularized by Thomas Harris’s 1981 novel Red Dragon and its 1988 sequel, The Silence of the Lambs. The latter novel is instigated through the “missing person” trope, wherein agents of justice must race against a clock to rescue a missing victim before they’re presumably killed by the novel’s antagonist. Similarly, The Fourth Monkey follows a detective as he struggles to find a teenager, Emory, before she dies of dehydration in the killer’s captivity.

These narratives are also often centered around a brilliant, taunting antagonist who engages a troubled but determined investigator in a high-stakes “cat-and-mouse” game. Barker employs this trope through the complex relationship between the killer, Anson Bishop, and Detective Sam Porter. The novel’s central mystery is propelled by Bishop’s direct communications, most notably the diary he leaves for Porter to find, which details his twisted upbringing and motivations. This plays on two tropes: the intelligent yet psychologically troubled villain and the unreliable narrator. These genre staples create a sense of instability and unpredictability for readers, as it’s never clear what is true or what the antagonist may be driven to do.

This diary has real-world parallels, such as the Zodiac Killer, who famously sent cryptic letters and ciphers to the San Francisco Chronicle newspaper during his 1960s and 1970s murder spree to taunt police and the public. Furthermore, Bishop’s ritualistic modus operandi—sending an ear, eyes, and a tongue to his victims’ families—reflects the concept of a killer’s “signature,” a term used in criminal profiling by the FBI to describe behaviors that fulfill a psychological need. By utilizing these familiar tropes, Barker grounds his narrative in a tradition that thriller audiences recognize, building suspense by playing with and subverting genre expectations while exploring the psychological depths of both the hunter and the hunted.