ObscureHollywood.net’s review published on Letterboxd :
Dr. Jekyll (Paul Massie) pursues his scientific experiments to the exclusion of all else, including his wife, Kitty (Dawn Adams). Kitty has compensated by taking a lover, Paul (Christopher Lee), a friend of Dr. Jekyll. Jekyll injects himself with his formula, and turns into Edward Hyde. Hyde, young and handsome, indulges his depraved tastes. Hyde, incapable of love or empathy, plots to free himself of Jekyll, Kitty, and Paul.
The psychological contrast of noble Jekyll versus depraved Hyde is retained, but the typical physical contrast is reversed; bearded Jekyll is weak and older looking than young, vigorous and handsome Hyde.
A good Hammer film.