The Red Right Hand

From fantasticfiction dot com: "Dr. Harry Riddle's first problem was the whereabouts of the grotesque hitchhiker who had vanished after killing Innis St. Erme. The second was what he did with St. Erme's missing right hand. Riddle's investigation reaches into the very core of madness, but it takes one further, horrific turn when he himself becomes implicated in the serial killer's trail of murders."