I came to this book in preparation to teach medieval history for homeschool. I've had to refer to the plot below, so if you don't want it given away, don't read further than this paragraph! But I gave this a four for 'not bad historical fiction' and a sound 2 for dodgy theology that interfered with my enjoyment of the book. Certainly I don't think one could call this a good Christian read (compared with, say, 'The Door in the Wall' or even 'If all the Swords in England').
Despite the reference to Thomas Becket, the only relevance is that Hugh's father has been hounded out of England as one of Becket's murderers. The value of the book is in the flavour of what medieval monastic life must have been like; medieval Glastonbury; the friendship between the two boys and some moderately exciting things that happen to them; and the book's link with the Arthurian Grail stories.
But there are downsides to the book. It is LONG (350ish pages, albeit quite big print). It has dated a little, mostly in its slow pace, and in its chapter headings which utterly kill all surprise- if you read the book, try hard not to notice them.
But my main problem with the story is that it is billed as 'living history' and yet involves Hugh seeing a vision of where Arthur is buried (which is shown as correct) and and in the final pages has a vision of the Holy Grail, the 'healing powers' of which cure his lameness.
Now, I can see the argument that runs: 'but this is what the medieval church was interested in'. But it's a matter of proportion: the quest for the Grail takes over the whole book under the guise of a 'holy' pursuit. It is folktales mixed in with Christian beliefs - tolerable in Arthurian legend; worse here.
Why this is stocked by Greenleaf Press (home of Reformed historical literature) beats me. I would find something else to read.