Santo and Blue Demon vs. the Monsters aka Santo y Blue Demon contra los monstrous sees wrestling’s finest team up to battle a whole host on monsters!
The film begins with two wrestling matches: a female tag-team bout, then Blue Demon and Juan Garza face El Gigante Ebano and El Arabe. Santo looks on. Meanwhile, the corpse of mad scientist Bruno Halder is placed in a crypt; his brother Otto and Otto’s daughter Gloria are the only mourners. As soon as everyone else leaves, the dwarf Waldo and three green-faced zombies break into the crypt and steal the body of their master.
Blue Demon advises Santo to stop worrying about Bruno and enjoy his vacation with Gloria; Blue himself departs for his holiday. However, as he drives along a deserted highway, he spots Waldo driving a horse-drawn wagon, with the body of Bruno and the zombies on board. Blue follows them to an old castle, and sneaks inside. Waldo uses Bruno’s own equipment to revive the mad doctor from the dead. One of the zombies spots Blue Demon and knocks him out. Bruno makes a duplicate of the wrestler and sends him out, with the zombies, to kill Santo.
Santo stops his car in the middle of the highway to kiss Gloria. Apparently desiring more privacy, they pull into a wooded lane and make out some more. However, Blue Demon and the zombies appear. Santo is knocked out and tossed off a cliff; Blue and the zombies kidnap Gloria and speed off in a car. Santo, who didn’t fall too far, gives chase in his fancy silver auto. Gloria manages to leap out of the zombies’ car into Santo’s.
Santo, Gloria and Otto Halder open Bruno’s coffin: it’s empty. “Perhaps your traditional rivalry provoked” Blue Demon into joining Bruno, Otto suggests. “We were only rivals in the ring, I can’t find any logical explanation [for his actions],” Santo says. Meanwhile, Blue Demon, Waldo and the zombies are recruiting monsters for Bruno’s gang: they collect a vampire man, and a skinny, ferret-faced mummy. Bruno also has a cyclops, a wolfman, and the Frankenstein’s monster.They are all revived and sent out to kill people.
The Cyclops is an amphibious creature, killing a fisherman who is working on his nets. Santo skin-dives and spots the monster on the bottom of a lake, but their battle takes place on dry land. After a struggle, Santo rams a wooden stake into the monster’s chest.
The Frankenstein’s monster attacks a young couple who are having a picnic. He steps on the boy’s face and carries off the girl. The werewolf kills a campesino and his wife. The vampire man bites a couple of young women who then join Bruno’s team.
The monsters and Blue Demon attack Otto, Gloria and Santo in the Halder house. Gloria, dressed in her baby-doll pajamas, flees outside, but the vampire man is scared off by a large stone cross. Blue Demon gets a telepathic message from Bruno, ordering him to return to the castle.
Santo is pitted against a “foreign” wrestler called El Vampiro. Coincidentally, it is Bruno’s vampire wearing a tiger-striped mask. He starts to bite Santo but Gloria runs up to the ring and her golden crucifix makes him turn into a bat and fly away. The other monsters show up and a battle royal erupts in the ring; the spectators run out screaming; the lights go off. But once again, the monsters shuffle back to the castle, looking rather sheepish at the fact that they can’t quite finish off Santo.
Later, Santo and his friends are in a restaurant. As soon as the floor show is over, the monsters attack again. This time, they manage to kidnap Otto and Gloria. The prisoners are taken back to the castle where Bruno prepares to kill them. But Santo planted a bug on Frankenstein’s monster; he arrives at the hideout, defeats the fake Blue Demon, and frees the friendly one. Together they wreck the lab, causing fires and explosions. Santo, Otto and Gloria escape as the castle goes up in flames.