After receiving an anonymous letter about a missing 12-year-old girl, devoutly Christian Police Sergeant Neil Howie (Edward Woodward) travels by seaplane to a remote Scottish island to investigate. But the islanders welcome neither his badge nor religious devotion, for Lord Summerisle (Christopher Lee) and his devoted followers worship only the pagan gods of old - and those gods demand a sacrifice. Howie fears for the missing girl's life and follows every possible lead to find her - despite the islanders' interference - before she becomes a human sacrificial lamb.