Joe goes undercover and he and his wife find the sleepy little town in which Mrs. Gillespie lives. Pretending to be interested in buying her house, Joe arranges to see Mrs. Gillespie. In the meantime, Joe's wife notices that a man keeps watching them. This same man is on the trail of Mrs. Gillepsie, Joe believes, as he overhears the man inquiring as to her whereabouts.
After Joe meets Mrs. Gillespie, who is much older than he anticipated, he finds her charming and is inclined to believe her to be harmless. However, before he leaves, an older gent walks into the house, and Mrs. Gillespie introduces him to Joe has her fiancé.
Alarmed, Joe leaves - only to find the other investigator waiting outside. Convinced that this investigator has been hired to follow him, Joe reacts defensively and abruptly leaves without speaking to the man. As Joe tries to figure out what to do, his wife urges caution. Later, Joe and his wife run into Mrs. Gillespie's new fiance while enjoying drinks. After inviting him to their table, it is discovered that he had had a physical the day before, at the insistence of Mrs. Gillespie. While he didn't mind the physical, he insisted that she have one as well.
Outraged at the thought of the poor old man walking into Mrs. Gillespie's death trap, Joe paces the hotel until he comes to the conclusion that he will confront the black widow. Upon arriving at her home, he is greeted by the real estate agent. She has already sold the house, married, and is off on her honeymoon. No one knows where the newlyweds have gone. Meanwhile, the investigator who keeps showing up arrives. Joe discovers that this man was not trailing him after all, but worked for an entirely different insurance agency - one that was investigating Mrs. Gillespie's new husband. Apparently, he had had four previous wives, each of whom died under mysterious circumstances.