When Martha Beck, an unmarried, 200-pound nurse in a Mobile, Alabama, hospital, sends her name in to a lonely hearts club, she receives a letter from Spanish immigrant Ray Fernandez. A meeting is arranged, and Martha is immediately attracted to the suave gigolo. She persuades Ray to invite her to stay at his home in New York, where he tells her of his practice of using his appearance and charm to persuade middle-aged women to part with their money. Soon Martha, posing as Ray's sister, joins her new lover in his travels. They start by swindling Doris, a New Jersey schoolteacher, but soon Martha's jealousy causes her to add murder to their list of crimes. When Ray marries Myrtle Young, a pregnant Arkansas woman, to obtain $4,000 for legitimizing the baby, Martha gives the woman an overdose of sleeping pills. Later, in Albany, Martha bludgeons to death rich widow Janet Fay while Ray strangles her. In Grand Rapids, Michigan, they move in with Delphine Downing, an attractive widow with a 2-year-old daughter, but when Ray gets the widow pregnant, the insanely jealous Martha shoots her and drowns the child. Aware that Ray has been consistently unfaithful to her, Martha telephones the police and discloses the murders. While awaiting trial, Martha and Ray correspond with each other, still avowing their love.