In the Middle Ages, historians told how in the 5th century the Holy Grail had been transported from the Holy Land to the last outpost of Roman civilization in Western Europe - the isle of Britain. The trail then went cold, but in this book the author tells how he carved out a niche for himself as an historical detective, researching overlooked ancient chronicles and then following a trail of mysterious clues left in the English countryside over the centuries. The result was his discovery of an artefact believed by some to be the Holy Grail.
Phillips takes a cluster of myths, legends, beliefs and tenuous historical connections that form the basis of the Grail stories. He then uses this to determine how they are based on a factual event which is the Grail arriving in England. With all these works there is always a high level of assumptions about what is factually true. For example there is a convent close to a historical site important to his thesis. Even though it is a couple of hundred years out, does not matter as it is highly probable the site has been reused for the same purpose over and over since the Romans arrived. That is where you question the rationale in the arguments and that is one of many examples. Phillips does solid research in examining all the various theories about Arthur and the Grail and adds his into the mix.