Santo vs. The King of Crime aka Santo contra el rey del crimen was an attempt to establish Santo as a legacy character – inheriting the mask from his fictional father (something he would reuse decades later in introducing his real son to the public – El Hijo del Santo).
As the film opens we meet a schoolboy named Roberto. Roberto witnesses a little girl being harassed by bullies and steps out of a group of classmates to help her. During the scuffle he gets a bloody nose. His father is mighty proud of him and initiates him into a secret: Behind a painting in his office hangs a silver mask. It is the mask of Mexican wrestler and heroic fighter against evil: Santo – El Enmascarado de Plata!
So the film establishes that for many years it was Roberto’s (fictional) father, who, as El Santo, confronted criminals of all kinds with courage and determination, and who had got the silver mask decades ago from his father and one day it will be Roberto’s turn.
After many years, it’s finally time that the now grown Roberto puts on the silver mask. Audiences were excited by this as they got to see El Santo unmasked – be it from behind.
He is then guided by the faithful servant Matias to a secret room in the basement of the house (Santo Cave?). Here is Santos headquarter, with radios and countless technological gadgets. From now on, a new Santo will take up the fight against evil. And the first challenge is already waiting… Virginia, a journalist of the daily newspaper “Novedades”, her friend, the policeman Fernando Lavalle and his assistant Conrado visit one evening a sporting event.
At the ballgame known as “Jai Alai”, Virginia observes three men in the hall that make suspicious hand signs to one of the players. Virginia suspects that the game should be manipulated and senses a big story. Fernando is skeptical and forbids her to carry out further research. But it soon turns out that her suspicion is correct. The crime boss Don Cosme and his minions manipulate the games to win large sums of money when betting.
Some time later Virginia reports a wrestling match between Santo and another wrestler by order of her publisher. Suddenly she discovers the same three men in the audience who she had already seen at the Jai Alai game. She observes that one of the men secretly put a liquid on Santos towel. Just in time, she can warn Santo, who then finds out that it is acid. As the crooks try to make off, there is a wild brawl between the gangsters and the police, but in the confusion the men escape.
From now on, not only the police but also Santo is interested in who is behind the machinations. Fernando and Conrado soon follow a clue that leads to the nightclub “Trocadero”. There they become witnesses as one of Don Cosmes henchmen try to persuade a Jai Alai player to manipulate a game, but the man refuses.
During the next game he is mortally wounded by a ball thrown against his head. The incident is classified by the police as an accident, but the truth is that the player Tony who is on Don Cosmes payroll killed the uncooperative player deliberately. A little later, as Santo tries to learn from Tony who is the mastermind behind the betting scams, Tony is shot from ambush.
By now, Don Cosme has enough of Santos interference with his lucrative business and he flies in a wrestler from Germany named Max Stromberg. He should fight against Santo in the ring to get rid off the masked wrestler once and for all. To be on the safe side, one of Don Cosmes men will shoot at Santo with a gun at a suitable moment. But the plan goes awry, however, and instead of Santo, Max Stromberg is fatally wounded. Don Cosme is not happy about this and as a last resort, he now kidnaps Virginia and Fernando to set a trap for Santo.
As Santo rushes to the aid of the two, Don Cosme and his men are already waiting for him. With a trick and his outstanding abilities Santo can finally overcome all gangsters and hand over Don Cosme to justice!