A backwoods game warden and a local doctor discover that giant leeches are responsible for disappearances and deaths in a local swamp, but the local police don't believe them.
A small town doctor mistakenly ingests an experimental drug made from the blood of vampire bats which transforms the kindly medic into a bloodthirsty monster.
A scientist develops a formula which will cause animals to regress to the form of their primitive ancestors, and tries it on himself with disastrous results.
Martians come to Earth to build an H-bomb strong enough to blast Earth out of orbit so that Mars can be moved into its place in closer proximity to the sun. Super-scientist Larry Martin, inventor of the first stratospheric-flight spaceship as well as a jet-powered personal flying suit with helmet, is called upon by the government to investigate ramped-up UFO reports occasioned by the Martians' spaceships. The Martians, meanwhile, led by Marex, engage a renegade earth scientist and a gaggle of gangsters to help them steal supplies, operate a menacing robot, and build their bomb. This movie serial in 12 chapters was originally planned as a sequel to "Radar Men From The Moon" with Commando Cody as the hero but at the last moment the main characters' names were changed and all other references to that serial removed from the script.
It is 1865 and Union prisoners use a military balloon to escape a Southern prison camp near the end of the Civil War. The balloon drifts for days and finally lands on a mysterious volcanic island with very unusual inhabitants. Also landing, in a better aircraft, is Rulu, a visitor from Mercury. She seeks a radio-active material that will enable her to manufacture an explosive that will destroy the world or, at least, the portion known as Earth in this 15 Chapter Serial from the 1950s.
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.
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.