In the small Italian village of San Stefano at the turn of the nineteenth century, small-time confidence man and former musician Conrad Ryler, who now calls himself Bruce Conrad, pays a call on the occupants of the Villa Francesca. They include the villa's owner, Francis Ingram, a partially paralyzed pianist, his beautiful nurse, Julie Holden, and his secretary, Hilary Cummins. When Bruce compliments Ingram on his powerful piano playing, Ingram, who only has the use of one hand, credits Julie's care and inspiration. Unknown to Ingram, however, Julie plans to leave her position. This news greatly upsets Hilary, as her presence frees him to continue his studies of astrology. That night, at a dinner attended by Hilary, Julie, Bruce and Ingram's lawyer, Duprex, Ingram asks his guests to testify to his sanity and then has Bruce and Hilary witness his will. Later, Hilary eavesdrops as Julie invites Bruce to leave Italy and start a new life with her. When Hilary reveals her plans to Ingram, Ingram calls him a liar and chokes him with his good hand. Only Julie's intervention saves Hilary's life. Later, Ingram wakes in the middle of the night and, failing to rouse Julie, wheels himself out of his room and accidentally falls down the stairs to his death. The funeral is attended by Ingram's only relatives, Raymond Arlington and his son Donald. To their dismay, Ingram's will leaves everything to Julie, who announces that she will accept the legacy and remain in Italy. Duprex then offers to help the Arlingtons contest the will for a third of the estate. That night, the villa's residents see a light in the mausoleum and later Ingram's distinctive arrangement of Bach is heard on the piano, although no one appears to be playing it. After Duprex' body is found nearby, the police commissioner discovers that Ingram's good hand has been cut from his body. The commissioner also reveals that the window of the mausoleum has been broken from the inside, and handprints have been left on the ground beneath. Meanwhile, Donald remembers a hidden safe in Ingram's study and tells Hilary that he is sure an earlier will is inside. After dark, Donald sneaks into the library, watched by the commissioner, and while the piano mysteriously plays, a hand reaches out and chokes Donald. The commissioner saves him from the attack, but later, as Hilary sits in the library, he sees a disembodied hand crawl toward him. Fearfully, he captures it and nails it to a board so that it cannot escape. In the middle of the night, Donald remembers that the combination to the safe is based on the number of bones in the hand. He, his father, and the commissioner open the safe and find the hand. In the confusion that follows, Hilary and Julie are left alone together. Julie asks Hilary to confess to the murder of Duprex and the attack on Donald, but learning that she has told no one of her suspicions, Hilary attacks her. Julie is saved when Hilary hears the piano playing. Now completely mad, he tries to burn the hand, but it chokes him to death. Later, the commissioner finds the wire that Hilary used to activate a recording of Ingram playing the piano and reveals that the appearances of the hand were all in Hilary's mind. The mystery solved, Julie turns the villa over to the Arlingtons and leaves with Bruce.