A series of bizarre murders in San Francisco forces an unlikely investigative duo to confront a killer who leaves behind a signature tied to a specific shade of blue. Hobart Lindsey, a seasoned police detective, and Marvia Plum, a sharp-witted private investigator, must navigate the city's social strata to uncover the motive behind these calculated crimes. As the body count rises, the pair faces internal departmental friction and the physical dangers inherent in tracking a predator who remains one step ahead. The narrative unfolds through a traditional mystery framework, balancing procedural rigor with the distinct personalities of its two leads.

This work is characterized by the classic tropes of the detective genre, emphasizing the interplay between two contrasting investigators. The narrative structure suggests a focus on the procedural aspects of crime solving, typical of mid-career mystery series from this era. Readers likely appreciate the established rapport between Lindsey and Plum, which provides a consistent anchor throughout the investigation. The tone remains grounded in the conventions of the hardboiled and police procedural subgenres, offering a steady, methodical look at the pursuit of justice in an urban environment.