Peredur, The Undiscovered Truth of the Nazi Grail Quest is written in two parts.

The first part of the book charts the life and adventures of Otto Rahn, the man tasked by the Nazis, in the 1930s, with finding and getting his hands on the Holy Grail for them. The Nazis were hell bent on finding the Grail and reuniting it with the Holy Lance in a bid to create a mythical past of the Aryan race. Rahn believed that by uncovering the truth behind the Germanic saga of Parzival he would discover the whereabouts of the Grail. Parzival had, according to legend, successfully completed a quest to find the Grail, whilst being a knight in the court of King Arthur. In dissecting the story of Parzival, Rahn concluded that the Grail had been held by the Cathars, a heretical Christian sect, in their fortress at Montsegur. He believed that the Grail was still there, waiting for him to find it and based his quest around this belief. Unfortunately, after chasing round Europe in his efforts to find the Grail, and coming within touching distance of finding the truth, the Nazis patience with him ran out with him, and Rahn came to a sticky end, without ever having found the Grail. Rahn was the real-life figure who inspired the fictional movie character Indiana Jones.

The second part focusses on Peredur, a British knight hailing from York, and the true hero of the original Grail Story. By examining the life of Peredur and the Grail Story, Peredur, the Son of Evrawc, written about him, we are able to reach the truth of the Grail Rahn and the Nazis never found. Rahn came very close to uncovering this, but the Nazis had lost faith in him, and casting him as a charlatan, hounded him to his death. Much of the story of Peredur, the Son of Evrawc is played out in the ancient British kingdom of Elmet, encompassing much of what we now call South Yorkshire, and whose southern border lay along the line of the River Don. As the story is unpicked, the truth of the Grail, is unravelled, leading to some astonishing findings.