Paul Naschy, the werewolf sensation of Spain, gets to strut his stuff and expand as an actor in this Leon Klimovsky film. Sure, we’re use to seeing Paul play Waldemar by now but he gets to branch out and show off his acting chops by also playing the sinister Mister Hyde in this film as well.

The lovely Shirley Corrigan travels to Hungary with her husband (Jose Marco) to visit his parent’s resting place but when their car is about to get stolen, Jose intervenes and is promptly murdered. Since Shirley Corrigan is all kinds of sexy, the murderers have other plans for her but Paul Naschy intercepts their decadent intentions and saves the blond beauty. Of course, as Waldemar, Naschy changes into a wolfman during a fullmoon and when Shirley spots his transformation she gets a plan.

Shirley takes Paul to London to visit a friend, Dr. Jekyll (Jack Taylor) who is the only man who can help Paul defeat his curse of lycanthropy. Dr. Jekyll has always had a thing for Miss Corrigan which upsets his raven-haired helper, Mirta Miller. When the good doctor spurns Mirta in order to help Paul and Shirley, Mirta kills Dr. Jekyll and plans to use Waldemar as a tool for mayhem. She uses a serum devised by Jekyll to turn Waldemar into Mister Hyde but when the fullmoon is out, Hyde’s influence clashes with the lycanthropy and makes Paul Naschy one mean dude.