Elliot Freeman, a war veteran with a family history of mental illness, becomes a pariah in his small town after his wealthy father suspiciously dies in a hunting accident with Elliot present. As a result, Elliot resides in isolation at his familial manor, and works as a portrait artist. While painting a model, Dolores Martello, Elliot is visited by his attorney, Adrian Benedict. Adrian presents paperwork for Elliot to sign regarding the payment of his sister Lynn's tuition.
Later at the local tavern, Elliot and Dolores's boyfriend Charlie get into a fight. Dolores leaves with Elliot, and in private she professes her love for him, recalling a previous sexual encounter they had six months prior. Elliot declines her, and she responds by telling him she is pregnant with Charlie's child; she threatens to spread rumors that the child is Elliot's. The two argue, and Elliot slaps her when she compares him to his "crazy" father. Later that night, Dolores is viciously stabbed to death by a cloaked figure.
Lynn arrives in town the next day from New York City to transfer to the local women's college. When Elliot brings Lynn to the college, he meets Carol Bishop, an instructor there and an old acquaintance who swiftly takes a liking to him. Meanwhile, police Lieutenant Palmer begins investigating Dolores's murder, questioning Elliot as well as Charlie, who is employed at the college as a handyman. Silvia, one of Charlie's side girlfriends, provides a false alibi for him. Adrian comes to Elliot's aid when police attempt to elicit a false confession from him. Later, while Charlie is working at the college, a female student, Alice St. Clair, makes sexual advances toward him, and the two have sex in a closet.
Lieutenant Palmer attempts to further close in on Elliot as a suspect in Dolores's murder, and Elliot confesses to Carol that he murdered his abusive father, and that Adrian helped get him acquitted. At the tavern that night, Charlie knocks Elliot unconscious before stealing his car to go skinny dipping at a lake with Alice. Silvia angrily witnesses Charlie leave with Alice. At the lake, Charlie admits he cannot swim, and Alice pulls him in the water anyway, resulting in them fighting. He punches her, rendering her unconscious, and subsequently drags her to the shore before fleeing in his car. When Alice regains consciousness, she is greeted by a cloaked figure who slashes her to death.
After news of Alice's murder is made public, Silvia becomes convinced Charlie murdered her, as well as Dolores. She calls Lieutenant Palmer and confesses she lied about Charlie's alibi, but before she can finish the call, Charlie attacks her, ripping out her earrings and beating her before fleeing on his motorcycle. A police chase ensues, but Charlie is apprehended. Elliot returns home and receives a phone call from Carol, but it is cut short when he is taken hostage by Adrian and his brutish chauffeur, Max, who are attempting to escort him to a mental institution. Carol arrives moments after they depart, and Elliot jumps from the moving car, managing to evade them by hiding in the woods. Searching for Elliot, Carol enters his mansion, followed by Adrian moments later.
In an upstairs room, Carol is confronted by the cloaked figure who attempts to stab her, but the attack is thwarted by Adrian and Elliot. Elliot chases after the assailant, who is revealed to be Lynn. Lynn crazedly explains that she committed the murders as she felt Elliot's attention was being taken away from her; she arrived in town the day before Dolores's murder, killed her, and then later mistakenly murdered Alice after seeing Elliot's car parked at the lake. She also admits to having fired the shot that killed their father, not Elliot. Later, with Lynn incarcerated, Elliot and Carol are able to reside happily.
The identity of the cloaked murderer is revealed after a series of killings, culminating in a final confrontation and resolution for Elliot and those around him.
The climax untangles the web of suspicion that has surrounded Elliot, shifting blame and resolution in a way that reflects the film’s ongoing theme of paranoia and mental illness. The conclusion underscores how fear and mistrust can poison relationships and reputations, even in close-knit communities, while nodding to the proto-slasher mechanics that would later define a whole genre.
