Lawyer Perry Mason believes Nadine Farr did not poison Mosher Higley. Under truth drug, she confesses to Dr Denair, who brings the tape recording to Perry. As usual, secretary Della Street and PI Paul Drake help, Lt Tragg and DA Burger hinder. Is the killer her fiancé Locke, Higley niece Sue Newburn and hubby Jackson, man of work Cap'n Hugo, or a nurse?