Dr. Jekyll believes good and evil exist in everyone and creates a potion that allows his evil side, Mr. Hyde, to come to the fore. He faces horrible consequences when he lets his dark side run amok.
After a young woman is coerced into prostitution and her brother framed for murder by an organized crime syndicate, retribution in the form of an ape visits the mobsters.
Kitty Carroll, an attractive store model, volunteers to become a test subject for a machine that will make her invisible so that she can use her invisibility to exact revenge on her ex-boss.
Dr. Paul Carruthers is frustrated because he thinks his employers, Mary Heath and Henry Morton, have cheated him out of the company's profits. He decides to get revenge by altering bats to grow twice their normal size and training them to attack when they smell a perfume of his own making. He mixes the perfume into a lotion, which he offers as a gift to Mary and Henry. When they turn up dead, a newspaper reporter decides to investigate.
Dr. Bernard Adrian is a kindly scientist who seeks to cure a young woman's polio. He needs human spinal fluid to complete the formula for his experimental serum. Meanwhile, a vicious circus ape has broken out of its cage, and is terrorizing the townspeople. Can there be a connection?
Dr. John Garth conducting an innovative medical experiment aimed at prolonging life and combating aging. The experiment takes an unexpected turn, placing the doctor in a confrontation with the ethics of his work and the consequences of his research.
Dr. Leon Kravaal develops a potential cure for cancer, which involves freezing the patient. But an experiment goes awry when authorities believe Kravaal has killed a patient. Kravaal freezes the officials, along with himself. Years later, they are discovered and revived in hopes that Kravaal can indeed complete his cure. But human greed and weakness compound to disrupt the project.
Four explorers are summoned to Peru by the brilliant physicist Dr Thorkel. They discover a rich source of radium and a half-mad Thorkel who shrinks them down to one-fifth their normal size when they threaten to stop his unorthodox experimentation.
A mysterious plague, the Purple Death, ravages the earth. Dr. Zarkov, investigating in his spaceship, finds a ship from planet Mongo seeding the atmosphere with dust. Sure enough, Ming the Merciless is up to his old tricks. So it's back to Mongo for Flash, Dale, and Zarkov.
When news reporter Walter Garrett arrives at the hotel room of bombshell actress Angela Merrova to conduct an interview, he finds her dead from multiple stab wounds. He returns with the police to find the hotel empty and the body vanished. Garrett writes about the incident but is fired when Merrova, alive and well, goes to the paper to complain. Now his only chance to get his job back is to find the truth, which involves the grisly scheme of a madman.
Dr. Henryk Savaard is a scientist working on experiments to restore life to the dead. When he is unjustly hanged for murder, he is brought back to life by his trusted assistant. Re-animated he turns decidedly nasty and sets about murdering the jury that convicted him.
One of the sons of late Dr. Henry Frankenstein finds his father's ghoulish creation in a coma and revives him, only to find out the monster is controlled by Ygor who is bent on revenge.
Feature version of the 1938 film serial FLASH GORDON'S TRIP TO MARS. Flash Gordon fights Ming the Merciless once again to ensure the survival of the Earth.
The second and final Grand National Pictures film to feature The Shadow, played again by Rod La Rocque. In this version, Lamont Cranston is an amateur detective and host of a radio show with his assistant Phoebe (not Margo) Lane. Cabbie Moe Shrevnitz and Commissioner Weston also appear.