Dr. John Garth, a noted scientist who is convinced that life cells are immortal and old age a disease, is on the verge of perfecting a serum that would defeat senility when he is condemned to hang for a mercy killing. In the prison laboratory, Garth feverishly works against time to perfect his serum. With less than a half hour to live, Garth persuades Dr. Ralph Howard, the prison physician, to inoculate him with the serum. Ironically, at the last minute, his sentence is miraculously commuted to life imprisonment, and Garth awakens from the effects of the serum to discover that he has conquered age and faces endless years in prison. The serum, however, has a more insidious effect on Garth, because the blood in the inoculation contained the cells of a confirmed killer, and soon the murder poison comes to dominate him, turning him into an involuntary killer. His first victims are Dr. Howard and a prison trusty, but because there were no witnesses, Garth is not suspected of the crime, and soon after, he is freed from prison for his noble experiments. After returning home to his daughter Martha, Garth invites several of his old friends to visit. He insists on inoculating them with his serum, and when they refuse, the scientist murders them one by one. When clues in the first murder point toward the doctor, Captain McGraw of the police department begins to watch the Garth house. Martha’s fiancé, Dr. Paul Ames, also notices the doctor’s suspicious behavior and warns her to leave the house. After nearly strangling his own daughter, Garth returns to prison to give himself up, but when he loses control and tries to strangle a guard, the guard shoots him, bringing Garth’s tormented double life to an end. More on Wikipedia or Mubi
Watch Before I Hang (1940)
