Dr. Courtine, an unworldly academic, is invited to spend the days before Christmas with an old friend. Twenty years have passed since Courtine and Austin last met, but the invitation to Austin's house in the Cathedral Close of Thurchester, is welcome, for reasons other than the renewal of an old acquaintance. Courtine hopes that the visit will allow him to pursue his research into an unresolved mystery, using the labyrinthine Cathedral library. If he can track down an elusive eleventh-century manuscript, the existence of which only he believes in, he hopes to dispose of a potentially deadly rival.

But as Courtine prepares to settle into his research, Austin tells him the story of thr town ghost, a story of duplicity and and murder two centuries old. The mystery captures Courtine's donnish imagination, as perhaps it is intended to do. Doubly distracted, Courtine becomes unwittingly enmeshed in the sequence of terrible events that follows his arrival, and he becomes witness to a murder that seems never to have been committed.