Agent Joaquin recalls his latest mission while lying wounded in an ambulance: Joaquin has infiltrated into a band of smugglers. When the villains learn the truth about him, they kidnap Jouqin's fiancee. Santo comes to her rescue and fights the band.

In his first film El Santo was still referred to as ‘El Enmascarado’. Rendered compliant by a scientist and his gangsters via a serum and mysterious rays, he is forced for the opening act to be a henchman for the evil forces who want to take over the world. The film has great historic value, due also to its impressive exterior shots of pre-revolutionary Cuba 1959.