Boris Karloff, Evelyn Keyes, Bruce Bennett, Don Beddoe, Edward Van Sloan, Ben Taggart, Pedro de Cordoba, Wright Kramer, Bertram Marburgh, Robert Fiske, Frank Richards, Kenneth MacDonald, Ernie Adams, Frederick Burton, Edward Earle
A physician on death row for a mercy killing is allowed to experiment on a serum using a criminals' blood, but secretly tests it on himself. He gets a pardon, but finds out he's become a Jekyll-&-Hyde.