A scientist working on cures for rare afflictions, such as a bone softening agent made from molds to allow him to correct the spinal deformity of his nurse, finds the physical causes of lycanthropy in wolf-man Larry Talbot and of vampirism in Count Dracula, but himself becomes afflicted with homicidal madness while exchanging blood with Dracula.
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.
Deranged scientist, Gustav Niemann, escapes from prison and overtakes the director of a traveling chamber of horrors, soon reviving the infamous Count Dracula, the frozen Frankenstein Monster, and the Wolf Man.
A fugitive, dangerous madman reaches an English village where he confronts his former partner who left him for dead in the jungle after their discovery of a diamond mine. When the former partner also claims to have since lost the mine and all its wealth, which he took all for himself, and though the partner is still living in a state of luxury , the madman takes up an offer from a crazed scientist to make him invisible, something the scientist has already done with experimental animals, so that he can take revenge.
Grave robbers open the grave of the wolf man and awaken him. He doesn't like the idea of being immortal and killing people when the moon is full so tries to find Dr. Frankenstein, in the hopes that the doctor can cure him. Dr. Frankenstein has died; however, his monster is found.
Frankenstein's unscrupulous colleague, Dr. Bohmer, plans to transplant Ygor's brain so he can rule the world using the monster's body, but the plan goes sour when he turns malevolent and goes on a rampage.
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. 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.
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.