The Coworker is a psychological thriller that utilizes established tropes to create a compelling mystery and an atmosphere of unease. A key feature of the genre is the presence of flawed and complex characters. McFadden provides two multifaceted protagonists in Dawn Schiff and Natalie Farrell. Both women have committed serious crimes, and the narrative provides extensive psychological insights into the sources of their fears and motivations. The dark side of human nature is also aptly represented in the mind games that Dawn plays with Natalie, for Dawn not only frames her coworker for murder; she also taunts her with silent phone calls and the mysterious appearance of turtle figurines. The novel therefore employs the classic “cat and mouse” scenario to heighten the narrative tension as Natalie attempts to discern and escape the traps that Dawn has set for her.

A further common conceit of the psychological thriller involves employing an unreliable narrator whose statements are deliberately designed to create false impressions and mislead the reader. Untrustworthy narrators add many layers of complexity to mysteries that are already convoluted and insidious in nature, and to further heighten the effect of this common stylistic device, McFadden provides two narrators who are unreliable for very different reasons.