Rose Elliot (Irene Miracle), a poet living alone in New York City, discovers an ancient book called The Three Mothers. It tells of the existence of three evil sisters who rule the world with sorrow, tears, and darkness. The book, written by an architect named Varelli, reveals that the three dwell inside separate homes that had been specially designed and built for them by the architect in Rome, Freiburg, and New York. Rose suspects that she is living in one of the buildings and writes to her brother Mark (Leigh McCloskey), a music student in Rome, urging him to visit her. Using clues provided in Varelli's book as a guide, Rose searches the cellar of her building and discovers a hole in the floor which leads to a water-filled ballroom. After accidentally dropping her keys into the water, she enters the flooded room. Swimming under the surface, she sees a portrait bearing the words "Mater Tenebrarum" and is able to reclaim the keys. A putrid corpse suddenly rises from the depths, frightening her. She escapes, although a shadowy figure watches her leave the basement.In Rome, Mark attempts to read Rose's letter during class. He is distracted by the intense gaze of a beautiful student (Ania Pieroni). When the class ends she leaves suddenly; Mark follows, leaving the letter behind. His friend Sara (Eleonora Giorgi) picks up the letter, and eventually reads it. Horrified by the letter's contents, she takes a taxi to a library and locates a copy of The Three Mothers. While looking for an exit, Sara is attacked by a monstrous figure who recognizes the book. She throws the book to the ground and escapes. Later that night, she seeks the company of a neighbor named Carlo (Gabriele Lavia) and both are stabbed to death by a gloved killer. Mark discovers the bodies and two torn fragments from Rose's letter. After the police arrive, he walks out of Sara's apartment and sees a taxi slowly driving by. In it is the music student, staring at him intently once again.Mark telephones Rose but is unable to hear her clearly. He promises to visit just before the connection fails. Cut off, Rose sees two shadowy figures preparing to enter her apartment. She leaves through a back door, but is followed. In a decrepit room, she is grabbed from behind by a clawed assailant and brutally murdered.Upon arriving in New York, Mark meets some of the residents of Rose's building, including a nurse (Veronica Lazar) who is caring for the elderly Professor Arnold (Feodor Chaliapin, Jr.), a wheelchair-bound mute. Mark learns from the sickly Countess Elise (Daria Nicolodi) that Rose has disappeared. Elise explains how Rose had been acting strangely. After the two find blood on the carpet outside Rose's room, Mark follows the stains. He suddenly becomes ill and falls unconscious. Elise sees a black-robed figure dragging Mark away, but the figure suddenly stops and gives chase to Elise. She is attacked by dozens of cats, who bite and claw at her flesh. The hooded figure then stabs her to death. Mark staggers to the house's foyer where the nurse and caretaker (Alida Valli) put him to bed.The next day, Mark asks Kazanian (Sacha Pitoeff), the antique dealer who sold Rose the Three Mothers book, about Rose. However, the man provides no information. That night, Kazanian drowns several cats in a Central Park pond and accidentally falls into the water. Hundreds of rats from a nearby drain crawl all over him, gnawing his flesh. A hot dog vendor hears Kazanian's cries and rushes over. The man kills Kazanian with a knife.Carol, the caretaker, discovers the horribly mutilated corpse of Elise's butler (Leopoldo Mastelloni) in the Countess' apartment. Shocked, she drops a lit candle which starts a fire. Attempting to put out the flames, she becomes entangled in burning draperies and falls from a window to her death.Meanwhile, Mark uses a clue from Rose's letter to discover that beneath each floor is a secret
Output: Who is found with rabid cats and is stabbed to death?