The novel’s characters, and with them the reader, learn of the possible existence of the Holy Grail (spelled Graal in the book) from a manuscript. Archdeacon Julian Davenant is preparing a set of lectures for publication. When Julian goes to London to visit his publisher, the editor Kenneth Mornington shows him a manuscript that includes an interesting entry, part of which Kenneth reads to Julian:

If we consider these evidences, and the hypothetical scheme which has been adduced, to account for the facts which we have . . . it seems probable that the reputed Graal may be so far definitely traced and its wanderings followed as to permit us to say that it rests at present in the parish church of Fardles.

Fardles is the popular rendering of the name of the village where Julian is Archdeacon; he prefers to use the correct, Latin name, Castra Parvulorum. Julian, on hearing this passage, reflects that there is a chalice in the church about which he has very little information and which has been replaced for general usage.

Gregory Persimmons, the retired owner of the publishing house, is also interested in the reputed Graal. It is gradually revealed that he dabbles in the occult and desires the sacred object for the power it reputedly contains. To get near the Fardles church, he buys a country home and takes up residence there. He soon visits Davenant at the church, with a request to purchase the chalice, telling him he heard they had an “extra” one and saying it is for a friend starting a mission church. When Davenant says no sale is possible, Persimmons tries to project an image of himself as harmless, seeming

the portrait of a retired townsman trying to find a niche for himself in new surroundings, shy but good-hearted, earnest if a little clumsy, and trying not to touch too roughly upon subjects which he seemed to regard with a certain ignorant alarm.

Gregory wants the chalice to use its power and enlists two equally evil-minded accomplices, Manasseh (called “the Jew”) and Lavrodopoulos (“the Greek”) to help him acquire it. However, they disagree about the reasons for doing so. They believe that its power is inherently good and, therefore, it must be destroyed to remove it from the arsenal of the powers of good. One of these villains, Manasseh, explains this to Gregory:

To destroy this is to ruin another of their houses, and another step towards the hour when we shall breathe against the heavens and they shall fall. The only use in anything for us is that it may be destroyed.

After Gregory acquires the Grail through lying about using it to cure Barbara of an illness that he himself has caused, he and the accomplices hide it in the Greek’s shop. Mornington and another ally, the Duke, find it there. The evil ones have secured it behind a ritual diagram; crossing one of its border lines proves fatal to Mornington, as the Duke observes his face in horror.

It was white and staring and sick with a horrible sickness; he shut his eyes before this evil. All the gorgeous colours and pomps of sin of which he had been so often warned had disappeared; the war between good and evil existed no longer, for the thing beneath the Graal was not fighting but vomiting. . . . Kenneth, gathering all his life's energy together, forced himself two steps nearer his aim, moaned as even that energy failed, dropped to his knees, and at last, choking and twisting, fell dead on the diagram.