Santo vs. Dr. Death aka Santo contra el doctor Muerte aka Santo Strikes Again, aka The Masked Man Strikes Again (English Dubs) starts with an intruder entering a Mexican art museum and, unseen by the guards, sprays a famous painting, called “Los borrachos” by Velázquez, with a substance that, when the painting is uncrated back in Spain, has damaged the artwork. Famous art expert and restorer Dr. Mann is asked to work on restoring the canvas. However, Mann and his gang are behind the vandalism: using a process that involves tumors extracted from models held captive in his basement, Mann makes an exact copy of the painting and then “exposes” this fraud to the museum authorities. Thus, he gets to keep the original in his private collection.
Santo, famous masked wrestler and international secret agent, is asked to investigate the crime, since he’s scheduled to wrestle in Spain anyway. He’s teamed up with Paul, another Interpol agent, who proves his worth when the two men are attacked by assassins in Santo’s hotel room. After an excellent brawl, Santo and Paul triumph. They investigate Dr. Mann, but can prove nothing, although one of Mann’s live-in models tells Paul that each time a model finishes her work, she disappears and is never heard from again.
Interpol agent Susan is sent to Mann’s castle, substituting for a real model. However, Susan and Ester are caught while snooping around Mann’s laboratory, and they are tossed into the dungeon with the other captives. Santo and Paul break into the castle and, eluding the various death traps, free the models. Sara, Mann’s assistant, falls into an acid bath used to dispose of dead bodies; Mann is captured. Santo pursues Peter, Mann’s chief associate. Peter tries to escape by motorboat, but Santo–dangling underneath a helicopter on a rope ladder–leaps into the boat. They fight, and Santo leaps overboard just before the craft smashes into the shore and explodes.