Holmes is one of three protagonists in Holmes, Marple & Poe. He derives his name and many of his characteristics from the Arthur Conan Doyle character Sherlock Holmes. Patterson and Sitts’s version of Holmes has a highly acute sense of smell, something that he finds useful professionally and often burdensome in his day-to-day life, as he frequently finds scents overwhelming.

Holmes responds to this sense of overwhelm by using heroin, which he likes for its ability to dull his senses. He also uses the drug to forestall panic attacks; this precipitates an overdose during the search of the Siglik house. Poe’s comment that Holmes was unconscious for over four minutes, his longest time to date, indicates that Holmes has suffered other overdoses prior to the novel’s start. Holmes promises his partners that he will cease using heroin at several points in the novel; inwardly, he recognizes that damaging his sense of smell (a possible side effect of taking the drug via his nose) will make him a less effective detective. Despite this, he continues to use the drug throughout most of the novel, culminating in self-harm via gunshot, which his partners assume to be an attempt to die by suicide.