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...

Mortmain, an accomplished musician and rare art collector, observes the research results of his friend, Dr. Pennison Crisp, who successfully grafts a paw from one cat onto another. After Mortmain becomes engaged to Bella Forsythe, the ward of his friend, banker Gordon Russell, to whom he owes money, Russell, in love with Bella, causes her brother Tom to disgrace himself, and forces Mortmain into bankruptcy. After Flaggs, the clerk of Russell's lawyer, overhears Mortmain say that he would like to kill Russell, Mortmain, learning that Russell has been mysteriously murdered, faints and injures his hand. Dr. Crisp anesthetizes Mortmain with ether, which causes hallucinations, and then tells him that although the hand must be amputated, he can graft another in its place. After Tom, the murder suspect, accepts Crisp's offer of $10,000 and dies during the transplant, Mortmain, with Tom's hand, gradually goes insane as Flaggs blackmails him and Bella recoils from his touch. As the hand uncontrollably chokes Flaggs, Mortmain awakens from his ether-induced dream. Tom is alive, and Flaggs confesses that he killed Russell after Russell ruined him financially.