Dr Jekyll and Mr Hyde (Heroes & Villains)

Dr. Jekyll has been experimenting with his identity. He has developed a drug which separates the two sides of his nature and allows him occasionally to abandon himself to his most corrupt inclinations as the monstrous Mr. Hyde. But gradually he begins to find that the journey back to goodness becomes more and more difficult, and the risk that Mr. Hyde will break free entirely from Dr. Jekyll's control puts all of London in grave peril.