Santo vs. the Killers from Other Worlds aka Santo contra los asesinos de otros mundos aka Santo vs. the Living Atom opens with four people being killed by a mysterious blob. Chief O’Connor of the national security police receives a call informing him of the crimes–this is so serious that only one man can solve it: Santo!
Santo arrives at the office; O’Connor tells him 4 people were murdered, but the cause of death is still unknown. Their bodies were horribly mutilated. 3 of the victims were important people in economic matters ; the last was driving a stolen car, and his identity is unknown. Santo: “This leads me to believe it is the work of a criminal, and not just an unfortunate occurrence.”
O’Connor and Santo receive a call on their private television communicator: Malkosh tells them that he wants $10 million in gold bars in 24 hours, or more will die. The Chief tells Santo, “We won’t permit blackmail. He must just be a maniac.” Santo : “Well, at least we have 24 hours to investigate.” However, 24 hours later nothing has been discovered. But no crimes have been committed. O’Connor: “Just as I thought, this was just someone who was taking advantage of our problems for his own gain.”
But another victim of the blob turns up on the street, and then the blob invades a lab and kills 3 people. The Chief doesn’t know what to do, he doesn’t know what to tell his superiors. Malkosh calls back: “You didn’t pay attention, and I did what I threatened. 3 scientists are dead.” Santo confirms this: Professor Chamberlain, his wife and daughter are dead. Malkosh says he still wants his gold: they have 48 hours to get it together, and he’ll tell them where to deliver it by plane. Although the Chief says “We can’t give in to this blackmail,” Santo disagrees. “We have no alternative, we have to pay. But I have a plan.”
The gold plane takes off, but radio contact is lost. Malkosh tells the pilots where to land, and he meets them, along with some henchmen. But Santo has been hiding on the plane, and he defeats the gangsters, only to be captured by Malkosh. The villain takes Santo to a hidden arena. “I let you live out of curiosity about the great Santo,” he says. “You have 3 chances to live.” Santo defeats two gladiators, and is then faced with a flame-thrower. Seizing a machine gun from one of the guards, he kills the bad guys, and wounds Malkosh. “You have defeated my best men,” the villain says, “but you are still only human.”
Santo takes Malkosh to a lab, where the villain shows him a moon rock under a glass dome. Malkosh kidnaped Professor Bernstein, who had been loaned the rock for his experiments. Inside the rock are dormant microorganisms which grow rapidly when exposed to air. “They are intelligent, voracious, and vicious. They grow to form a giant creature, like a cancer.” Bernstein wanted to use the lunar creature to help humanity, but Malkosh wanted to blackmail the world.
Bernstein is a prisoner of Malkosh’s ex-partner, Boris Licur, who wants to conquer the world with the moon germ. Meanwhile, the moon rock has spawned another blob, and it gets Malkosh. Santo escapes in the plane. He radios O`Connor: “I had to leave the gold. It’s safe, but we can’t get it right now. A monster from another galaxy is the murderer. Notify national security.” Meanwhile, Santo is going to try to find Bernstein.
Santo meets Karen, Bernstein’s daughter. He says he will help her find her father. Licur and his men attack them, but are defeated. One of the henchmen is captured and interrogated at police HQ, but he won’t talk. Licur, however, leaves nothing to chance. All of his henchmen wear neck-bands which contain poison gas, released when Licur touches a button on his wrist-band. He gasses his own man. Karen is kidnaped by Licur and his men, and a neck-band is put on her lovely neck.
Santo and O’Connor find the dead man in jail. “There goes our only clue,” O’Connor says. No, Santo replies: the man has traces of a special kind of soil on his shoe. It is only found in a sparsely-populated area of the mountains near here. Santo goes alone to find Licur’s hideout. He must find Bernstein quickly in order to save the world from the moon blob. But he finds out Karen has been kidnaped.
The Professor tells Licur it’s too dangerous to use the moon blob. Licur says you must tell me how to control it, or Karen will get the poison gas. Although the Professor says he doesn’t know how to control the blob, Licur gives him 10 minutes to come across with the information. He locks them in a small room. Licur and his female assistant read Bernstein’s notes, but they only say that the moon rock must be kept out of air in order to keep the germs dormant. Santo has arrived at the hideout, but his appearance is discovered by Licur’s men. After a titanic battle, he enters the house, only to see the blob has been set free. Santo lets the blob get Licur, but he frees Bernstein and Karen from their neck-bands. The trio escapes from the house when the blob eat Licur’s men.
Pursued across country by the blob, Santo and his friends take refuge in a cave filled with noxious gas. The wrestler tells Karen and the Professor to swim to safety via an underground river, and he ignites the gas in the cavern, trapping the blob in an airless hole forever.