A sea captain about to be hanged for a murder he didn't commit is rescued from the gallows by two of his crewmen. They head for the island of Pulinan, where they believe the real murderer--the captain's former partner--is hiding so the captain can clear his name. As it turns out, their troubles are only beginning

Although ostensibly the grand-son of the legendary hero, Clayton Moore's Ken Mason is little more than a cowboy in a black mask in this 12 chapter Republic serial. Mason, the head of the telegraph line work crew, assumes his ancestor's trade-mark mask (but not whip) in order to prevent a local czar (Roy Barcroft) from sabotaging the burgeoning telegraph line. Pamela Blake, a brunette starlet formerly known as Adele Pearce, played Mason's imperiled girlfriend, and the serial also benefitted from the usual competent work of Republic's great stunt-performers, including Dale van Sickel, Tom Steele, Eddie Parker, and Joe Yrigoyen.

A famous scientist invents a humanoid robot (the titular "monster"), so a greedy rival scientist plans to steal it for use in his criminal plans. His henchmen often kidnap a trained gorilla (the titular "ape") from the zoo, to aid in the schemes.

Based on a successful comic book that began in 1941, the Blackhawks were seven flyers who banded together during WW II to fight the Nazis. After the war, they continued to fight evil where ever they find it. In this movie, they are battling a group of spies and saboteurs bent on destroying democracy. The Blackhawks foil a succession of plots, with a cliff hanger ending in each episode.

A team of two-fisted insurance investigators (one of whom disguises himself as The Masked Marvel) endeavor to discover and thwart the loathsome saboteur Sakima.

A federal agent's life is in danger when he's exposed while investigating a parole scheme.

Novice policemen Stan and Ollie bungle a burglary investigation.

A private detective is approached by a wealthy entertainment executive to stop a blackmail scheme against him. Although he hasn't decided to take the job, the blackmailers believe that he already has, and he is marked for murder.