 Sylvia Welles asks Rip Conners to bug her apartment and make a bogus tape as a joke. She invites her boss, Richard Vanaman, over to work on a project. Vanaman discovers the bug and makes threatening remarks, but Welles blames it on a jealous husband. Later, Vanaman realizes he has lost a special coin in the apartment and goes to recover it, where he finds Welles dead and flees. Vanaman consults Perry Mason about claiming an unusual coin that was found in a parking meter. When he tries to retrieve the coin, Vanaman is arrested. Perry and D. A. Hamilton Burger each use the fraudulent tape to prove his case.