When the unscrupulous Carlos Manning discovers that an old Spanish land grant recently unearthed will leave a huge section of California real estate to the heirs of Don Quantero, he employs Mel Donovan and his killer henchmen to murder them all. That will leave Manning as the sole heir to millions. However, Delores Quantero tumbles to this plot and enlists the aide of two-fisted reporter, Cliff Roberts to save all her relatives

Jean Evans of an international wildlife foundation, who is known to Africa as 'the Panther Girl' because of her bravery in jungle living, stumbles on a plot by a mad scientist to frighten the natives out of a diamond-laden district by chemically growing crayfish to giant size, and enlists the aid of a game hunter friend to prevent a monster rampage and bring the culprits to justice.

Superhero Captain America battles the evil forces of the archvillain called The Scarab, who poisons his enemies and steals a secret device capable of destroying buildings by sound vibrations.

Jerry Blake (aka Federal Operator 99) teams-up with Joyce Kingston to thwart the plans of escaped crime boss Jim Belmont.

Beyond Hell's Gate Pass is territory controlled by a man who calls himself King Carter; he uses a variety of schemes to prevent the railroad from being built, for fear it will finish his control of (what he considers) his land.

A Martian invader crashes his spaceship conveniently close to the workshop of a scientist who is developing an interplanetary craft. If the extraterrestrial Purple Monster can complete the rocket ship and return to Mars, he will be able to start a full-scale invasion of Earth. Good thing Craig Foster sets out to thwart the Monster's mission!

Claire Forrest seeks her kidnapped scientist father, hidden somewhere on Mystery Island. He is held and forced to work on diabolical inventions by Captain Mephisto, a costumed villain.

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.

Fletcher Christian successfully leads a revolt against the ruthless Captain Bligh on the HMS Bounty. However, Bligh returns one year later, hell bent on revenge.

A new town doctor arrives at the same time as local Indians needprotection from troublemaking looters.