An evil scientist plots to take over the world from his base in Africa, where he has invented a machine that can cause earthquakes.

Police detectives battle the League of Murdered Men, a gang of resurrected dead criminals.

An evil scientist known as "Mr. M." uses a drug he has developed called "hypnotreme" to help steal submarine equipment. Federal agent Grant Farrell is dispatched to find the mysterious villain and stop his nefarious plans.

A police detective goes undercover and joins a gang of Nazi agents using explosive gases and artificial lightning to sabotage the war effort, whom he battles in disguise as The Black Commando.

Secret Service Major Steel (Joseph W. Girard), is one of the few men in America aware of the fact that Captain Albright (Dave O'Brien) is also Captain Midnight, daring masked aviator dedicated to fighting gangsters and enemies of America. When murderous bombing attacks are made on West Coast munitions plants, Steel sends for Albright and asks him to track down the mysterious Ivan Shark (James Craven), the foreign agent mastermind behind the attacks. Shark has learned about an ingenious range finder, invented by John Edwards (Bryant Washburn, and makes plans to obtain a model of the invention. Edwards instructs his daughter, Joyce (Dorothy Short), to bring the model to Albright for safekeeping in his mountain laboratory. Shark takes Edwards prisoner by Albright assures Joyce that her father will be saved and an end put to Shark's reign of terror. Dressing as Captain Midnight and enlisting the aid of his friends, Chuck (Sam Edwards) and Ichabod Mudd (Guy Wilkerson), Captain Midnight delivers on his promises fourteen chapters later.

Buck Sherman and Jake Jackson, a couple of evil carpetbaggers, illegally enter a Navajo reservation to prospect for gold and end up killing Aranho, the Navajos chief. Black Arrow, presumed Aranho's son, refuses to kill the Indian agent, Tom Whitney, in revenge, as demanded by Navajo law. Then, he is driven off the reservation for his reluctance to kill Whitney and decides to join forces with Pancho, Mary Brent and the agent to go in search of the men who killed the chief.