An enigmatic stranger called Mr Pye arrives on the Isle of Sark. Having arranged to stay with the formidable Miss Dredger, he starts on the wrong foot by inviting Miss George, a loathed neighbour of hers, to ride with them in the horse and carriage. As he gets to know the other residents, such as the lovelorn artist Thorpe and free spirited Tanty, he begins to take over the running of Dredger's home, much to her annoyance. But as she gets to warm to Pye, she inquires why he has come to the island, and it is then that he tells her of his plans to convert the heathen islanders to the love of who he calls 'Pal'.

Having persuaded Dredger to invite George to stay at her home, Pye has plans for George when he arranges a picnic on the beach for the residents to showcase the power of faith. But his plans are diverted when Tanty spots something in the water when in a tryst with a lover in the caves nearby. Later, Pye meets a naked Tanty walking back from a swim, but when he offers his shirt to cover her, she notices two marks on his back. He examines them the next morning to discover that he beginning to grow wings, but his attempts to try and remove them backfire badly.

Pye's attempt to rid himself of his wings by behaving badly goes spectacularly wrong, with George dying of a heart attack while also frightening both Dredger and Tanty. After his behaviour at George's funeral alienates many locals, he confides in Dredger of his secret that he has grown wings. Agreeing with him that he must do bad – or even evil – in order for his wings to disappear, he sets about doing so around the island. But while it begins to work, his actions have a peculiar side effect on him, while his odd behaviour causes some to call for his removal and confront him.

Dredger, Tanty and Thorpe are stunned when Pye reveals he has grown horns as a result of his bad behaviour to remove his wings. Reckoning that he is being punished by 'Pal' for not being humble in his preaching, Pye decides he needs to suffer humiliation at the hands of the island residents at the Cattle Show for his curse to be removed. But Dredger and Tanty have fears over his plans, which prove well founded when his appearance at the Cattle Show cause locals to fear that he is a devil, putting Pye's life in grave danger.