Mortmain is an accomplished musician and rare art collector. He is greatly impressed when his friend, Dr. Pennison Crisp, successfully grafts a paw from one cat onto another. Mortmain’s engagement to Bella Forsythe is complicated by the fact that she is the ward of his friend, banker Gordon Russell, to whom he owes money. Worse, Russell is also in love with Bella. Russell causes Bella’s brother, Tom Forsythe, to disgrace himself, and forces Mortmain into bankruptcy. Mortmain rashly says that he would like to kill Russell, but this is overheard by Flaggs, who works for Russell’s lawyer. Mortmain then hears that Russell has been murdered, and in shock he faints and injures his hand. Dr. Crisp anesthetizes Mortmain with ether, which causes hallucinations, and creepily tells him that although he must amputate the hand, another can be grafted in its place. Tom Forsythe, who is suspected of the murder, agrees to Crisp’s offer of $10,000, but dies during the transplant. Crisp now grafts Tom’s hand onto Mortmain’s arm. Mortmain gradually goes insane as Flaggs blackmails him and Bella is now afraid to be touched by him. The hand goes crazy! Mortmain awakens from his ether-induced dream to find that Tom’s hand is choking Flaggs…