Dr. Frankenstein and her assistant, Dr. Yanco, are going to bring one of their experiments to life in Santo Vs. Frankenstein's Daughter. She intends to use a monster named Ursus to do her evil bidding. Using a youth serum to retain their vitality, the doctors set their sights upon none other than El Santo. They need his super human blood to regenerate a stronger youth serum. They kidnap Santo's goddaughter, Norma and lure him into Dr. Frankenstein's lab where he is captured and enslaved. Will Santo make it out alive?