Shaffer read the David Pinner novel Ritual, in which a devout Christian policeman is called to investigate what appears to be the ritual murder of a young girl in a rural village, and decided that it would serve well as the source material for the project. Pinner had originally written Ritual as a film treatment for director Michael Winner, who had John Hurt in mind as a possible star. Winner eventually declined the project, so Pinner's agent persuaded him to write Ritual as a novel instead. Shaffer and Lee paid Pinner £15,000 () for the rights to the novel, and Shaffer set to work on the screenplay. He soon decided that a direct adaptation would not work well, so drafted a new story based only loosely on the story of the novel.
Shaffer read the David Pinner novel Ritual in which a devout Christian policeman is called to investigate what appears to be the ritual murder of a young girl in a rural village and decided that it would serve well as the source material for the project Pinner had originally written Ritual as a film treatment for director Michael Winner who had John Hurt in mind as a possible star Winner eventually declined the project so Pinner's agent persuaded him to write Ritual as a novel instead Shaffer and Lee paid Pinner £15000 () for the rights to the novel and Shaffer set to work on the screenplay He soon decided that a direct adaptation would not work well so drafted a new story based only loosely on the story of the novel