What gives El Santo, "the multitude's idol", his amazing power? How is he able to get up so quickly after being thrown down so violently? How can he recover so expertly after a receiving a flurry of strong blows? The answer is in his blood, and Dr. Frankenstein knows it.
The daughter of the famous Dr. Frankenstein, alive today because of an age-stopping serum she has developed, needs Santo's regenerative blood to perfect the now failing potion before she ages and dies. She'll get him by nabbing his hot girlfriend and using Truxon to defeat him when Santo comes to the rescue. Truxon is this big half man half gorilla monster created by...well...by injecting gorilla blood into a man. That's really all it takes, people.
Frankenstein's Daughter possesses villains that are actually interesting to watch, who don't serve instead as mere fodder for El Santo's panther-crushing arms. They demand pathos, they suffer, and merely seek to stay alive. Even what's usually just a host of generic henchman are sympathetic and interesting - they live in fear of Dr. Frankenstein's power, and are presented as individual people with differing personalities. The lead henchman seems to have genuine concern for Dr. Frankenstein, and may in fact be in love with her. A more memorable example is the eye-patch wearing henchman that can't take part in Frankenstein's plot to send a freshly hypnotized girlfriend to claw out Santo's eyes. He can't guard Santo because he can remember what it was like to lose his own eye when he was young. It's indicative of the effort that was put into this Santo installment, and it really works to produce what I consider the best kind of B-movie - the sort that takes itself seriously enough to garner emotional investment from its audience.
Most interesting for me was Ursus, a frankensteinian monster that poses a terrible threat to Santo and his compatriots when the gorilla-man Truxon fails. The interesting part is that after Ursus takes a terrible wound and is left for dead, Santo finds him again later, suffering horribly and near death. Santo takes pity and uses his shirt to bandage the monster up. Santo tells the monster that he'll come back for him when Dr. Frankenstein is defeated, and when Santo can't seem to move the heavy gravestone that hides the entrance to Frankenstein's base, the monster, in terrible pain, does it for him. He secretly follows Santo and his companions and gives more aid at an integral moment, at the cost of his face. You'll see why. When Frankenstein's base starts to collapse, Santo doesn't want to leave the monster, but realises that his suffering must come to an end. Fantastic stuff.
Oh, and something I think I keep forgetting to mention is how awesome the soundtracks are in Santo movies. Swingin', ultra groovy tracks that usually kick the film's mood off accompanied by colourful opening credit sequences that really encapsulate the era they come from. Frankenstein's Daughter provides no less.
So: Another really cool Santo film, and the first directed by Miguel M. Delgado. Probably the best of the ones I've watched, though Santo and Blue Demon vs. Dracula and the Wolfman (also Delgado) comes a very close second for sheer awesomeness.