Dora Baldini, Marco, and Bruno Baldini move back into Dora's former home, a place heavy with memories from a marriage to Carlo. Carlo, an abusive heroin addict, was thought to have killed himself at sea after his boat was found adrift, a tragedy that lingered over Dora and contributed to a nervous breakdown and a period of psychiatric care. With Bruno away as a commercial airline pilot, Dora is left alone with Marco and haunted by fragmented recollections of the past, memories intensified by the electroshock treatments she endured while institutionalized.
Marco begins to experience unsettling events within the house and appears inexplicably drawn to the basement. Dora notices drastic shifts in Marco's behavior and is shaken to discover he has shredded her underwear. Disturbing signs multiply, and she pleads with Bruno to leave the house, but he remains unmoved. While Bruno is on a flight, Dora finds a bundle of roses with a note addressed to her from Carlo. Suspecting Marco wrote it as a twisted joke, she confronts him, only to be met with denial.
Dora takes Marco to a psychologist friend, Aldo Spidini, for examination. Aldo suggests that Dora's trauma from her marriage to Carlo might be coloring her perceptions and projecting anger onto Marco, though Dora confesses a troubling belief that Marco is being possessed by his deceased father. One afternoon, Dora witnesses the piano playing by itself and sees drawings in Marco's room levitating, yet she cannot locate Marco. She eventually finds him in the den, where he asks why she killed his father, triggering a repressed memory in which Dora recounts slitting Carlo's throat after he forcibly injected her with heroin and LSD.
Distraught by the memory, Dora is reassured by Bruno that Carlo killed himself and that her recollection is only a delusion. Yet she remains convinced that Carlo haunts the home and possesses Marco. Dora awakens in the middle of the night to banging noises from the basement, and when she investigates, she finds Bruno smashing down a brick wall. Carlo's corpse has been hidden behind the wall, Bruno reveals, and he explains that he helped her cover up the murder years ago by stashing Carlo's body and releasing his boat to sea, staging the disappearance as a suicide. He adds that they had to return to the house to prevent Carlo's remains from being discovered if they sold it; once the remains are relocated, they can leave. In a frenetic act of rage, Dora swings a pickaxe at Bruno, impaling him and stuffing his corpse into the open wall alongside Carlo's.
Dora rushes upstairs to find Marco but instead encounters a ghastly apparition of Carlo in his bed. In the hall, Marco appears again, charging toward her, but when he reaches her he transforms into Carlo and embraces her, sending Dora into a panic. She tries to flee, but violent poltergeist activity traps her inside the house. Returning to the basement, she watches as the furniture seems to move of its own accord, and she slashes her own throat with a boxcutter while Carlo's hand grips the knife. Outside, Marco sits at a backyard table, sipping tea with his father's invisible ghost and then gives the ghost a gentle push on the tree swing.
