After her first two husbands die under mysterious circumstances, Mrs. Marguerite Gillespie (Gladys Cooper) prepares to marry for a third time. Suspecting that Mrs. Gillespie has knocked off her previous spouses for their insurance money, detective Joe Rogers (Steve Forrest) inaugurates an undercover investigation. Despite all the evidence, Joe ultimately cannot bring himself to believe that Mrs. Gillespie is a murderer -- but, of course, this is Alfred Hitchcock Presents, and there has to be a murderer somewhere.