Aztec gold is tempting for the secret society Colonel Ramirez works for. And Don Carlos Fuentes wants to avenge Carlos, his nephew. Together they enlist the illusionist Steve Dickart, alias Mephisto, into their service. He and his sister Lily will seek information and sow discord at the Mexican border. They know that sooner or later there will be a secret agent of the rangers in their path. And they all have old scores to settle with Tex Willer! Having escaped Mephisto's first trap, Tex goes on the counterattack, going to find Don Carlos Fuentes and his gang in their refuge on the Devil's Mesa, where they hide the gold stolen from the Aztecs. Meanwhile, at Fort Tampico, Lily seduces and draws to her side a young officer, Lieutenant John Roller, who is now willing to do anything for her... Having recovered the gold and defeated Don Carlos Fuentes' gang, Tex and old Tom have no choice but to have Mefisto imprisoned in Fort Tampico. But they didn't take into account the special powers of their little sister Lily Dickart... The situation is reversed for our heroes and Tex, in prison for high treason, is sentenced to death! Having crossed the border with Ed Colton's smugglers, Tex meets the guerrilla leader who is fighting against the conservative army that deposed the legitimate president. Montales promises Tex to help him find Mephisto. In exchange, Tex works out with him the strategy to lead a victorious revolution, and sets off with Montales' lieutenant, Drigo, to defeat an entire garrison alone. Where is Montales? The elusive guerrilla, fighting against the tyrants who oppress Mexico, seems to be found everywhere, at the head of his valiant rebels. The truth is that there are two of them, perfectly identical, with a black mask on their faces, and one of the two is a gringo we know. Only Steve Dickart, alias Mefisto, has understood who the second commander of the guerrillas is... and a long-distance duel of cunning begins between him and Tex
