American scientist Stephen Reinhart arrives in the remote English village of Arkham to visit his fiancée, Susan Witley, and her parents. Her disabled father, Nahum Witley, tries to discourage him from seeing her, but Stephen eventually reunites with Susan. Later, Susan's mother, who is bedridden, urges him to take Susan away. Stephen notices that her face is covered with a heavy, black veil. After Witley's manservant dies under mysterious circumstances, Stephen begins to suspect that something evil is happening in the house and to its occupants.
Susan's mother has become a disfigured mutant who tries to attack Stephen and Susan, but she disintegrates into a pile of ashes. Stephen soon discovers that the inhabitants of the house are slowly turning into monsters because of radioactivity from a fallen meteorite. Realizing his mistake in experimenting with the meteorite, Witley tries to destroy it, but he is turned into a mutant himself. Without reason, he tries to kill the lovers, but he falls down the stairs and disintegrates. As the house burns, Susan and Stephen escape to safety.