"Dr. Anna Kane has designed a computerized implant that monitors a psychopath's murderous rages. Subway killer John Chester Marlon is the principal subject of this experimental technology. But Marlon escapes the maximum security hospital, dragging Anna with him into New York City's dark underbelly ... -- container."
"Murderous rages, forcing him into unconsciousness whenever he gets the urge to kill. Then it all goes wrong. Despite the implant, the brilliant, handsome, twisted Marlon escapes from a maximum security hospital, dragging Anna into underground New York City subway and train tunnels and sewers - where Anna will truly understand the mind of a murderer."
"A thriller combining advanced medical computer technology with a portrait of a psychopath unrivaled in fiction, Nine levels Down visits twin hells: one in a man's mind, and the other under New York City. John Chester Marlon is the Subway Killer, known to have murdered at least 3 women, and sentenced to life in prison. Marlon is the principal subject of a ground breaking experiment. Dr. Anna Kane has designed a computerized brain implant that monitors a psychopath's."
"Dr. Anna Kane's computerized brain implant experiment on the psychopathic Subway Killer goes terribly wrong. When he escapes from a maximum security hospital he takes her with him down into the depths of the New York subway tunnels and into the mind of a murderer."@en

Nine levels down