The movie opens with Martha Beck (Shirley Stoler), a supervising nurse in a hospital located in Mobile, Alabama. She confronts two of her subordinates caught in a brief romantic moment in the lab, unleashing her bitterness and frustration on them. Overweight and emotionally isolated, Martha channels her loneliness into her job, cruelly belittling those she oversees, while at home, she takes care of her elderly mother, Dortha (Dortha Duckworth), who affectionately continues to refer to her as her "little girl." Martha's friend, Bunny (Doris Roberts), believing that a man would solve Martha's problems, unexpectedly submits an application for her to a lonely hearts club.
Initially irked by Bunny's actions, Martha soon finds herself correspondingly enamored with a charming man named Raymond Fernandez (Tony Lo Bianco). After exchanging letters for weeks, Raymond visits Martha, igniting an immediate sexual relationship. In a startling and twisted move, Martha gives her mother a sleeping pill to create privacy for herself and Raymond while they engage in intimacy just yards away from her mother, who is slumbering on the couch.
Upon his return to New York, Raymond asks Martha for a small loan and indicates he can no longer continue their correspondence, which devastates Martha. Desperate, she enlists Bunny's help to stage a suicide attempt to win back Raymond's attention. Truly flattered by Martha's display of devotion, Raymond invites her to New York, where he reveals his true conman identity—he preys on lonely women from various leagues, swindling them of their money and possessions. Despite his deceit, Martha's bizarre loyalty and willingness to forgive captivate Raymond, who hints at marrying her someday.
Back in Mobile, when Martha's supervisor discovers a letter indicating her relationship with Raymond, Martha lashes out, resigning under the claim that she is heading to New York to marry him, demanding her final paycheck be made out to "Mrs. Ray Fernandez." Continuing to deceive her mother and Bunny, Martha fabricates that she and Raymond have already wed. When Raymond learns of this deception and insists that Martha cannot bring her mother with them to New York, he chillingly suggests that she should eliminate her. Heartbroken, Martha enacts this plan by committing her mother to a rest home, despite her desperate pleas.
Martha and Raymond swiftly turn to swindling women, beginning with a desperate schoolteacher. Raymond introduces Martha as his "sister" during their honeymoon phase of deceit, but when they target a spirited Southern woman named Myrtle Young (Marilyn Chris), things take a dark turn. Myrtle hires Raymond to act as her husband in a ruse to salvage her family's reputation due to an unplanned pregnancy. However, Martha’s jealousy flares when Myrtle's affections for Raymond become evident, culminating in a venomous confrontation that ultimately leads to Myrtle's demise by Martha's hand.
Their con continues as they meet Evelyn (Barbara Cason), a wealthy older woman, but her arrival stirs Martha’s insecurities. This volatile love triangle only intensifies when Martha, brimming with jealousy, attempts suicide, only to be saved by Raymond, who comforts her.
As their financial resources dwindle, they look to exploit Janet Fay (Mary Jane Higby), a bank account-rich widow in her seventies. Employing their deceptive charm, they manipulate Janet into believing she is marrying Raymond, all while planning to abscond with her life savings. However, their lies begin to unravel, and Martha's mounting frustrations lead to fatal consequences. In a climactic rage, she strikes Janet with a hammer under Raymond's eerie encouragement, ultimately leading to Janet's death.
Their grim trail of deceit continues as they move into the home of Delphine Downing (Kip McArdle) and her young daughter, Rainelle (Mary Breen). When Delphine confides her pregnancy to Martha, revealing that she and Raymond have been intimate, the jealousy fueled within Martha spirals into lethal action. After cruelly attempting to abort Delphine's baby, Martha is pushed to violent extremes, ultimately leading to both Delphine and Rainelle's tragic demise.
As the film draws to a close, Martha, now incarcerated, awaits her trial—her only connection to Raymond being a touching letter of twisted devotion he has sent her. The narrative concludes with a haunting note, indicating that both Martha and Raymond faced execution for their gruesome crimes at Sing Sing prison. The story showcases a chilling exploration of love entwined with manipulation, betrayal, and fatal consequences.
