The story is set in the tiny, decaying cathedral city of Saint-Bertrand-de-Comminges, at the foot of the Pyrenees in southern France. An English tourist spends a day photographing the interior of the eponymous cathedral and is encouraged by the sacristan to buy an unusual manuscript. This, he concludes, had been created long ago, by canon Albéric de Mauléon (an invented character, said to be a collateral descendant of the real 16th century bishop Jean de Mauléon), who had cut up volumes in the old cathedral library. A disturbing illustration in the back of the book is a key to the story's suspenseful arc.
