The Midnight Man — Loren D. Estleman

Private eye, Amos Walker, repays a debt when a police sergeant, Van Sturtevant, is shot trying to help two colleagues who had been ambushed. Sturtevant and his wife hire Walker to find the people responsible, but Walker ends up in a race with a bounty hunter who is prepared to kill. Loren D. Estleman is the author of seven other Walker novels, including "Motor City Blue".