Dr. Jekyll is experimenting on human nature, believing every individual has a good and evil personality that can be chemically brought forth. Jekyll tests a serum on himself, releasing his vicious alter ego, Mr. Hyde, on 19th-century London. Prowling the town, Hyde ventures to a music hall and encounters Ivy, whom he takes forcefully as his mistress. After the serum's effects wear off, Jekyll vows never to take it again. But Hyde may not be gone for good.