The English Franciscan monk Roger Bacon was a famed but controversial scholar of originality and excitement. So much so that he was excommunicated and imprisoned by the Pope and only released shortly before his death in the early 1290s. Bacon claimed to have studied and seen many marvels of nature and science and concealed these in a book written in an unbreakable code called the 'Secret of Secrets'.

Sir Hugh Corbett, Keeper of the Secret Seal of Edward I of England, has been instructed by his King to organise agents in Paris to steal this Book of Secrets. They do so but pay a bloody, violent price. However, the French King Philip IV, for reasons best known to himself and his cunning henchman Amaury de Craon, now wishes a meeting between the scholars of England and France to discuss the possibility of breaking the code of the Book of Secrets. Edward I has no choice but to allow the Sorbonne's leading scholars to meet with his own clerks, led by Corbett, at Corfe Castle in Dorset. Such a meeting, Edward I realises, is demanded by the great Peace Treaty between England and France, which is only seven months old.

The meeting takes place at Corfe and the castle becomes a place of murder, mystery and mayhem. Young women from the castle are being slain whilst, in the nearby forest, the outlaw Horehound is deeply concerned by the horrors he has seen there. The situation becomes more serious when two of the French scholars die in rather sinister circumstances. Corbett and Ranulf-atte-Newgate have to thread this maze of malevolent murder whilst, at the same time, trying to decipher the great secrets of one of England's most outstanding scholars.