A dollar bill is only worth a dollar because we, as a society, acknowledge that fact. We've assigned worth to it and to make things work in life we all pretend that that small sheet of paper and ink is worth one dollar despite how much it actually cost to produce it. This sort of high-school philosophizing is the basic premise behind The Wicker Man whose underlying theme is that "the law" and "religion" only function when everyone around you has the same set of fundamental beliefs.
Edward Woodward (who would later go on to play TV's "The Equalizer") is Scottish cop who receives a mysterious letter begging him to help find a missing child. The child lives on the remote island of Summerisle and Woodward flies out to begin his investigation. There he finds the entire population are members of a pagan religion who revel in drunken orgies and ritual sacrifice. The group's leader is played to the hammy hilt by Christopher Lee. If you're looking for a movie with lots of bizarre Summer of Love residue mixed in with the love affair the early 70's had for Satanism (Rosemary's Baby, Mephisto Waltz, The Exorcist, etc.) this is your film.
Woodward's character a devout Christian and virgin is stymied over and over by the island's residents who refuse to acknowledge the child's existence despite his finding more and more evidence to support his believe that the child is in grave danger. He is also, as a devout and virginal Christian, tempted over and over by the sexual rituals going on all around him - most notably in a very very weird sequence where Brit Ekland does some sort of ritualistic nude dance in the room adjoining Woodward's. It's strange and weird enough to be creepy as shit. Eventually Woodward comes to the conclusion that the child is going to be sacrificed at the "May Day" ceremony that is coming up soon and he tries desperately to stop the event.
The Wicker Man is one of these movies that is critically lauded by just about everyone, and while it's not a bad movie by any stretch of the word, the hype and acclaim is has piled on it year after year is not justified. It's simply not an amazing film nor is it even an amazing horror film. It's good, but not mind-blowing. Worth seeing, but really only once. It's smart and well done, but not genius or classic. But recommended.
Also, Iron Maiden has a song called "The Wicker Man". It's ok. Reminds me of "I Wanna Make You Scream" by Battalion of Saints.