The Wicker Man wiki

Howie spends another night at the inn, where Willow openly attempts to seduce him. The next morning, discovering that his plane has been sabotaged, Howie elects to search the island for Rowan himself. He ties up the innkeeper and assumes his place as Punch, a principal character of the May Day festival. Disguised, he joins the procession of islanders as they cavort through the town and perform harmless sacrifices to various gods. Rowan is finally revealed, tied to a post. Howie cuts her free and flees but after a brief chase, emerges at another entrance where Summerisle and his followers stand waiting for them. Howie is shocked to see Rowan merrily embrace her captors and then notices that he is being surrounded.
Lord Summerisle explains to Howie that he was lured to Summerisle by the islanders, who have been successful in a conspiracy to lead him to believe that a missing girl was being held captive, and confirms to him that last year's harvest failed disastrously. Their religion calls for a sacrifice to be made to the sun god. Howie's devout Christian lifestyle and his livelihood as a policeman mean that he meets the outstanding criteria for a human that is to be sacrificed to appease the gods and provide a successful harvest.
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