Marlene Cowley wants to hire Spenser to investigate her husband, Trent Cowley. She is convinced he is cheating on her and wants proof that will humiliate and destroy him in open court. Spenser reluctantly agrees as he does not care for this type of cases and such proof isn't required in the courts of today. Before long, Spenser discovers that his client has a tail of her own. Apparently Trent shares the same concerns and has hired another investigator to tail her. The two investigators as a matter of professional courtesy acknowledge each other's case but neither can explain why there soon appears to be yet another investigator involved. Spenser begins looking at that angle and before he can get very far, the deaths begin. The two investigators soon vanish and Spenser is left working a case that grows stranger by the day.