A drifter with a deadly secret ignites passions in two lonely women.

Thirty-five-year-old spinster Maura Prince works part time as a speech therapist, spending the rest of her time caring for her tyrannical, blind, and invalided adoptive mother Edith Prince at Edith's musty old mansion in the country. Although Maura's supervisor at the hospital, Dr. Robinson, has asked her to work full time, Edith forbids Maura to consider his offer, sealing the issue by clutching at her heart after suffering an anxiety attack brought on by the thought of Maura leaving her side. The next morning, as Maura is vacuuming the house, Billy Jarvis, an itinerant young man, arrives on his motorcycle and tells Maura that he has been sent by the nephew of their neighbor, Mr. Bolton, to inquire about a job as a handyman. Although Maura is opposed to hiring the young stranger, Billy wins Edith's sympathy by cajoling her with stories about taking care of his invalid mother and asking to accompany her to church. Impressed by the boy's piety, Edith declares that some of her relatives were named Jarvis and therefore Billy must be her grandnephew. Edith hires Billy and tells him to move into Maura's room, thus displacing Maura from her own quarters. Despite Maura's misgivings, Billy turns out to be an industrious worker, patching up the moldering old house. One day, while Maura is serving Billy some tea, he asks her about the slight limp she has in her leg. When Maura explains that it is the result of a brain aneurism she suffered several years ago, Billy assumes that Maura is in her fifties and wonders why she allows Edith to bully her. Quietly offended, Maura tells Billy that Edith adopted her from an orphanage when she was fifteen years old, and that five years later, Maura walked out on her. Billy slowly wins Maura's confidence, and when he panics about fulfilling his promise to attend church with Edith on Sunday, fearing that there "could be trouble," Maura soothes him into going. At the service, Billy notices Mary Wingate, a young nursery school teacher, and afterward, watches as she drives off in the nursery school van. Later that night, Billy slips out of the house and rides his motorcycle to Mary's house. Along the way, he recalls being a boy in the farmyard where a number of women are jeering at him, accusing him of impotency. Upon arriving at Mary's house, Billy sneaks into her room, murders her, and after dressing her in a dress and shoes, loads her corpse onto the back of his bike and drives to a construction site, where he buries her body. The following day, as Billy works on restoring the arbor, Maura brings him some tea and they begin to chat. Soon after, Millicent McMurtrey, Edith's nosy friend, comes to visit and observes Maura and Billy together. Next, Mr. Bolton arrives with news of Mary's murder. Bolton continues that six other young women have been murdered in the vicinity within the last three months, all killed in their own bedrooms, all wearing shoes and dresses when their bodies were found. One day, the district nurse comes to discuss Edith's weakened condition with Maura. After advising more rest for Edith, the nurse leaves the house, and Billy opens her car door for her. Before driving away, the nurse asks Billy to tell Maura that she will return later that night to check on Edith. Later that evening, Edith awakens from her sleep and calls for Billy. When she tries to climb the stairs to his room, she suffers a heart attack, after which Maura calls for an ambulance to take them to the hospital. After the ambulance has departed, the nurse arrives at the house, and Billy tells her that Maura and her mother have gone to the hospital. When the nurse departs, Billy follows her on his bike, and after remembering being taunted and slapped by a prostitute, he kills the nurse and buries her body. Meanwhile, at the hospital, Dr. Robinson assures Maura and Millicent that Edith is out of danger and offers to drive them home. Declaring it improper for Maura to stay at the house alone with Billy, Millicent insists that Maura come to her house for tea. There, when Millicent chides Maura for her impropriety, Maura lashes out that she has stopped caring what her mother thinks. Maura bitterly recalls that when she was twenty, she ran off with a young man before Edith could scare him off like she did Maura's other boyfriends. They were planning to marry when Maura suffered her aneurism, and once she became ill, he left her. Maura returns home just as Billy comes back from killing the nurse. To prevent Maura knowing that he left, he breaks the bedroom window and after climbing in, pulls off his clothes. When Maura comes to his bedroom door, Billy greets her in a sweat and, claiming that he had a nightmare about his mother dying in flames, begs her to stay with him. As Maura tries to comfort the whimpering Billy, he cries out that he does not know what he is doing until it is too late and pleads with her not to leave him. In response, Maura promises never to do anything that might "take him away." The following day, when Maura visits Edith in the hospital, Edith insists that Maura throw Billy out of their house. When Maura replies that if Billy goes, so does she, Edith breaks into histrionics, accusing "her own daughter of deserting her." Retorting that Edith never let her forget that she was not her daughter, Maura walks out of the room. At a news kiosk, Maura sees a headline about the disappearance of a local nurse, and although she suspects that Billy is involved, she withdraws her savings from the bank. After having her hair cut and styled and buying a new wardrobe, she returns home and tells Billy she loves him. Declaring that she does not care what he did, Maura proposes that they go away to the highlands of Scotland. Some time later, after buying a farm on the Scottish coast, they settle into domestic contentment until one evening, while walking along a path, Maura encounters a young woman looking for her dog. When the woman says she stopped at the farm to ask Billy about the dog, Maura, worried that Billy's psychotic tendencies may have returned, hurries home to look for him. Discovering that Billy has gone, Maura wanders the bluffs above the sea. Soon, Billy drives up on his motorcycle, a crazed look in his eyes. Removing his goggles, Billy mouths a plea for Maura's forgiveness. As Maura watches with tears running down her cheeks, Billy revs up the bike's engine and crashes through the guard railing, plunging to his death.