Matthew Fred Holbert is a boy whose life is brutally shaped by a tragedy: as his father works on a tractor, the boy accidentally starts it and fatally injures his father, while his own left hand is mangled in the process. This traumatic event lands him in a psychiatric hospital, where doctors replace his ruined limb with a hook. Eighteen years later, Matthew is released and returns home to find that in his absence his mother has married a neighbor, Mack Parsons, Robert Knox. The new family setup unsettles him, and he wrestles with disturbing, incestuous feelings toward his mother even as he recoils from sex. In a furious act born of jealousy and rage, he murders Mack Parsons with an axe. When his mother discovers the crime, a heated argument ends with her knocked to the ground and dying after striking her head on a rock.
The next morning, a distraught Matthew hitches a ride with a young couple, whom he murders in rapid succession: he beats the man’s head with a rock and drowns the woman in a roadside stream. He drifts into a town where he encounters Vera, a painter and prostitute who Leigh Mitchell reminds him of his mother. Vera becomes the central fixation of his disturbed mind, and his obsession grows ominously as he fixes on her. His passion boils into violence when he slits the throat of one of her clients, a drunken sailor, Ron Bastone in a fit of jealousy.
Seeking to bind Vera to a life with him, Matthew bluffs his way into a mansion where he brutally murders the owner by smothering him with a pillow, hacks the maid to death with a cleaver, and even beheads the pet dog. He eventually brings Vera to the mansion, but she resists his attempts to control and possess her, prompting him to imprison her. He also bluntly brutalizes a visiting doctor, who had come to check on the owner, while Vera watches the horrifying scene. Vera senses his deep-seated discomfort with sexuality and uses it to her advantage, coercing him into an attempted sexual encounter. While he is momentarily distracted, she stabs him with a loose door hook and tries to escape; Matthew catches her and rips her throat out with his hook.
With Vera dead, Matthew’s grip on reality unravels completely. He runs through the town, haunted by visions of his victims, until he breaches a church. Surrounded by the phantoms of those he killed, he ends his own life with a fatal strike of his hook.
