A young Canadian nurse (Betsy) comes to the West Indies to care for Jessica, the wife of a plantation manager (Paul Holland). Jessica seems to be suffering from a kind of mental paralysis as a result of fever. When she falls in love with Paul, Betsy determines to cure Jessica even if she needs to use a voodoo ceremony,…

American psychologist John Holden arrives in London to participate in a symposium aiming to expose witchcraft and devil-worship as a fraud, with attention centered on a cult run by a Julian Karswell. Debarking his plane, Holden learns that the symposium leader, Henry Harrington, has suddenly died and he is now in charg…