Camouflage
Bill Pronzini Audio Book

David Virden's case is simple enough: find his ex-wife and deliver some papers to her. But she refuses the papers, sends a message to Virden to never contact her again, and slams the door. His colleague, Tamara, tells Nameless that Virden threatens to sue, stops payment on his checks, and claims that the woman they located isn't his wife. Then he disappears and his fiancée hires Nameless to find out why. Clearly, someone is trying to make Nameless the monkey in the middle.