Edward Woodward plays a pious police detective who is called to a remote island to investigate the disappearance of a young girl; when he gets there, no one will admit any knowledge of her. As he delves deeper into the close-knit community, he is shocked to witness the residents' decidedly un-Christian way of life, with schoolkids being taught about phallic symbolism, people holding open-air orgies in the night, and pub-dwellers singing saucy sex tunes. He begins to suspect that the girl has been offered up as a pagan sacrifice.
This type of thing has been done many times to varying degrees of success ("Twin Peaks" and The Village both have similar elements), but the surreal elements of The Wicker Man are hard to top the viewer is equally confused and on-edge as the morally upstanding detective. Several scenes involve long folk songs being sung by peripheral characters (one features a fully nude Britt Ekland cooing and writhing around her apartment), and this at first seems misguided and campy, but as the film progresses, the unusual deployment of music becomes integral to the story.
Christopher Lee is in top form as kooky yet commanding Lord Summerisle, the leader of the community that may or may not be a cult. The mystery builds up nicely to a wild pagan ritual that causes you to lose all your bearings for a good long while, until a grand and brutal climax reveals all. The final scene is as striking as any movie ending I can think of.