Actress Yvonne Orlac rests after her final performance at the 'Théâtre des Horreurs' (syled after the Grand Guignol) in Paris, France. As she listens to her husband Stephen Orlac play the piano on the radio, she is greeted by Dr. Gogol, who has seen every show featuring Yvonne, and unaware of her marriage, is aghast to learn that she is moving to England with her husband. Gogol leaves the theater heartbroken, buys the wax figure of Yvonne's character, refers to it as Galatea (from the Greek myth), and arranges that it be delivered to his home the following day.
Stephen Orlac is on a train journey from Fontainebleau to Paris, where he sees murderer Rollo the Knife thrower, who is on the way to his execution by guillotine. Gogol later witnesses the execution, along with the American reporter Reagan. Orlac's train crashes later that night, and Yvonne finds her husband with mutilated hands. She takes Stephen to Gogol in an attempt to reconstruct his hands, and Gogol agrees to do so. Gogol uses Rollo's hands for the transplant, and the operation is a success.
The Orlac couple are forced to sell many of their possessions to pay for the surgery, while Stephen finds he is unable to play the piano with his new hands. When a creditor comes to claim the Orlacs' piano, Stephen throws a fountain pen that barely misses his head. Stephen seeks help from his stepfather, Henry Orlac. Henry denies the request, upset that Stephen did not follow in his line of business as a jeweler. A knife thrown in anger by Stephen misses Henry, but breaks the shop front's window.
Gogol meanwhile asks Yvonne for her love, but she refuses. Stephen goes to Gogol's home and demands to know about his hands, and why they throw knives. Gogol suggests that Stephen's problem comes from childhood trauma, but later confirms to his assistant Dr. Wong that Stephen's hands had been Rollo's. Gogol then suggests to Yvonne that she get away from Stephen, as the shock has affected his mind and she may be in danger.
She angrily rejects Gogol, whose obsession grows. Henry Orlac is murdered, and Stephen receives a note that promises that he will learn the truth about his hands if he goes to a specific address that night. There, a man with metallic hands and dark glasses claims to be Rollo, brought back to life by Gogol. Rollo explains that Stephen's hands were his, and that Stephen used them to murder Henry.
Stephen returns to Yvonne and explains that his hands are those of Rollo, and that he must turn himself in to the police. A panic-stricken Yvonne goes to Gogol's home, and finds him completely mad. Gogol assumes that his statue has come to life, embraces her, and begins to strangle her. Reagan, Stephen and the police arrive, but are only able to open the observation window. Stephen produces a knife and throws it at Gogol, then finds his way in. Gogol dies as Stephen and Yvonne embrace.
Florence Crewe-Jones provided MGM with an original translation/adaptation of Renard's story "Les Mains D'Orlac". Writer Guy Endore, who worked with director Karl Freund on early drafts. Producer John W. Considine Jr. assigned the continuity and dialogue to P.J. Wolfson, and John L. Balderston began to write a "polish-up" of the draft on April 24, 1935. Balderstone went over the dialogue with Lorre in mind, and at points called for the actor to deploy his "M look". Balderston continued his re-write three weeks past the start of filming.
Filming started on May 6, 1935 with Chester Lyons as the cinematographer. Freund insisted on Gregg Toland, whom he got for a reported "8 days of additional photography". Actress Frances Drake recalled difficulty between Freund, Toland and Considine. Drake said that "Freund wanted to be the cinematographer at the same time", and that "You never knew who was directing. The producer was dying to, to tell you the truth, and of course he had no idea of directing."
Several titles for the film were announced, and on May 22, 1935, MGM announced that the title would be The Hands of Orlac. The Mad Doctor of Paris was also suggested, but the studio eventually settled on the original title of Mad Love. Shooting finished on June 8, 1935, one week over schedule. After the initial release, MGM cut about fifteen minutes of scenes from the film. Cut scenes included the surgery to get Rollo's hands, a pre-credit warning scene similar to the one in Frankenstein, and Isabel Jewell's entire portrayal of the character Marianne.
Mad Love was released in the United States on July 12, 1935 and, as Hands of Orlac, in the United Kingdom on August 2, 1935. The initial critical reception was focused on praise for Lorre's performance. The Hollywood Reporter said that "Lorre triumphs in a characterization that is sheer horror", Time magazine called him "perfectly cast", and Charlie Chaplin called him "the greatest living actor". Mad Love was not a hit at the box office, and had a small domestic gross of $170,000. Its foreign gross was larger, at $194,000.