A young girl has been reported missing on Summerisle, a remote Scottish Island and Sergeant Howie is sent to investigate. On arriving on the Island Howie sees how the islanders live and is a bit unnerved because they are all weirdo's in their own rights. No one knows who the missing girl is and Howie is sent on a wild goose chase by the islanders trying to get to the bottom of it. He eventually seeks out Lord Summerisle (Christopher Lee)who is also barking mad, and learns that the islanders live by different rules and philosophies which Howie very strongly disagrees with (being a devout, virgin christian). The apple crop of Summerisle failed the year before and the islanders want to make a sacrifice to the sun god's to ensure it does'nt happen again. Howie, we learn, has been lured to the island as the perfect sacrifice with the pretence of investigating the missing girl. In the end he get's sacrificed in the Wicker Man.
Incidentally, you can visit the remains of the Wicker Man on Burrow Head, in Galloway, South West Scotland.