Sergeant Neil Howie receives an anonymous letter from Summerisle, an isolated community famed for its produce, saying that a girl named Rowan Morrison has been missing for months. Upon arriving by seaplane, he’s baffled when everyone insists Rowan doesn’t exist, including the woman named in the letter as her mother, May Morrison, and all he gets out of May’s present Myrtle is that Rowan is the name of a hare in a nearby field.
Howie checks into an inn for the night, where everyone mocks him by launching into a bawdy song about the innkeeper MacGregor’s sensuous daughter Willow, while he notices pictures from every year’s harvest except the most recent, which is claimed to have broken. At dinner, he’s surprised to find all the food is cheap canned goods despite the island’s reputation, while his devout Christian sensitivities are assaulted when he finds several couples having sex out in the open, followed late at night by a nude Willow pounding on his wall with a sexually tempting song he just barely resists.
The next day Howie explains to Willow that he’s engaged, and doesn’t believe in premarital sex in any case, to which she advises him to leave before the upcoming May Day celebration. He visits the local school, passing another sexually explicit song accompanied by children around a Maypole, and even finds the teacher giving lessons about the importance of sex to the village’s religion. Once again, everyone claims not to know Rowan, but Howie forces his way into examining the class list and finds her name. The teacher explains that in their pagan religion, people are reincarnated as animals after death, which is then considered their true form.
Howie finds a grave for Rowan in the cemetery, but the groundskeeper insists he needs permission from their leader Lord Summerisle to dig it up and confirm her death. Outside Summerisle’s mansion he sees several women in a nude fertility ritual, and is further shocked at the Lord’s casual attitude to the paganism. Summerisle explains that his grandfather revitalized the island’s agriculture with crops specially designed for its climate, and introduced paganism back to its culture to ensure cooperation from the locals, which his father and now him have kept up.
After getting permission, Howie finds a hare in Rowan’s grave, and Summerisle refuses to give any kind of explanation. Howie becomes frustrated enough to break into the photography studio and finds a negative of the latest harvest festival, revealing that the harvest was very poor, explaining all the canned food. It also shows Rowan as the central figure of the festival, and after some research into pagan traditions, he deduces that she’s been locked away ever since the festival to be sacrificed on May Day to convince the gods to again give a good harvest.
Howie attempts to leave to bring a full force of police to search the town, but finds his plane has been sabotaged. He resolves to find Rowan himself, and his search includes eavesdropping on a preparation for May Day where Summerisle indeed promises there will be a sacrifice. He tries to convince May to save her daughter, but she only replies that he can’t understand sacrifice. After hours of searching, he takes a brief rest at the inn, where he overhears MacGregor and Willow attempting to put him under a sleep spell with a Hand of Glory. He promptly knocks out MacGregor and uses his Punch the Fool costume to infiltrate the May Day Parade.
Rowan indeed makes an appearance at the end of the parade when Summerisle calls for a sacrifice, and Howie fights his way to her and helps her escape through a cave. However, Summerisle and May are waiting on the other side and Rowan happily reunites with them as she’s assured she did her job perfectly. Summerisle reveals that the entire community created the deception of Rowan’s disappearance to lure Howie to the island, having determined him to be an ideal sacrifice to appease the gods after the failed harvest due to being a virgin and having a “king’s authority” with his job, as well as arriving to the sacrifice field as a “fool” of his own free will.
Howie insists the failed harvest was due to the specialized crops finally breaking down after a century, and even says that after they inevitably fail again, only Summerisle himself will be seen as a proper sacrifice to return them. Summerisle is clearly stricken at the idea, but still confidently says the sacrifice will work. Howie is thrown inside a giant “wicker man” statue with several animals, which is then set on fire. As his death approaches, he achieves a moral victory by defiantly shouting out a Christian psalm over the villagers’ pagan singing, and with dignity asks to be accepted into Heaven.
