At its core, "The Surgeon" is a classic cat-and-mouse chase between a determined detective and a brilliant but deeply disturbed killer. The novel delves into the minds of both hunter and hunted, building suspense as Rizzoli closes in on the Surgeon while facing her own demons. The narrative expertly portrays the meticulous planning and chilling precision of the Surgeon's crimes, contrasted with Rizzoli's unwavering commitment to justice.

Gerritsen masterfully explores the psychological impact of violence and trauma on both the victims and those who pursue justice. Detective Rizzoli carries her own baggage from a previous case, and her pursuit of the Surgeon forces her to confront those inner demons. The novel delves into the psychological complexities of survival, resilience, and the long-lasting effects of traumatic experiences.

Obsession is a driving force throughout the novel. The Surgeon is fixated on recreating a horrific medical procedure, while Rizzoli becomes consumed by the need to stop him. Gerritsen explores the fine line between dedication and obsession, showcasing how easily passion can morph into something dark and destructive. This theme is further amplified by the introduction of other characters whose own obsessions intertwine with the central plot.