Santo vs. Blue Demon in Atlantis aka Santo contra Blue Demon en la Atlántida sees Santo return to the Science Fiction genre with sprinkling of James Bond thrown in (and a ton of stock footage!)
Former Nazi scientist Hugo Ulrich–now calling himself “Aquiles,” in homage to the ancient Greeks whom he reveres–threatens the world with a nuclear holocaust unless he is acknowledged as the big boss. If he gets his way, the inferior peoples will be enslaved by his new master race. The world security organization learns that Professor Gerard has invented a device that will nullify Aquiles’ threat, but Gerard has to be kept alive in order to put the plan into effect. Only secret agent Santo knows Gerard’s identity and whereabouts. Aquiles sends some of his agents from his secret, underwater headquarters, to locate Gerard.
In the middle of a wrestling match with Santo, Blue Demon is drugged and kidnaped by Aquiles’ men. Blue is taken to the hideout and, when he refuses to join the new master race, is hypnotized by a big flashing disco ball and sent back to the surface to fight Santo. In the meantime, Santo learns that secret agent Pierre Duval is a traitor. Duval takes a high dive out of the window of Santo’s apartment.
Santo and Blue Demon tangle several times. Santo is aided by blonde agent X-25, who eventually reveals herself to be Circe, one of Aquiles’ flunkies. Taken to the underwater hideout, Santo is hypnotized and sent back to find Gerard. The evil Santo wrecks Gerard’s lab–only it isn’t Santo, it’s an impostor, who fights the real Santo and is killed. Santo explains that Juno, one of Aquiles’ followers who has switched sides, kept him from being hypnotized and helped him escape. However, now that Gerard’s equipment is ruined, they have to go back to Aquiles’ headquarters and blow it up in order to prevent the holocaust. Blue Demon is de-hypnotized by Gerard and joins them.
Eventually, the two masked wrestlers, Juno, and the scientist get into the underwater city and plant the bomb. Aquiles gives the order to fire the missiles he gets ready to drop a big bust of some Greek guy on Santo’s head, but Blue Demon spears him with a javelin. Aquiles turns old and wrinkled as he dies. Juno is mortally wounded saving Santo, and she gets old and dies. Santo, Blue Demon, and Gerard escape as the underwater city blows up.