Philip Sinclair’s grandmother has recently died. She leaves him the unusual legacy of the translated journal of his ancient ancestor, who was one of the four Cathar perfecti who escaped from the castle of Montségur with the ‘treasure of the Cathars’ strapped to his back – a treasure which has never been found. She also leaves him a sum of money with the request that he travels to the Pyrenean fastness of le Bézu where she believes the treasure still lies.
Meanwhile the famous young French archaeologist Jaqueline Blontard has arrived at le Bézu to start excavations as part of her new television series about the Albigensian Crusade. She believes her team will have the summer to uncover the secrets of the place before they are disturbed by the press and the authorities.
However the Roman Catholic Church already knows about their plans and has arranged for their agent to join the archaeologists. Also a secret but very influential body in Paris is sending their man to watch the excavations. Furthermore a criminal gang in Marseilles has become involved in the search for the treasure.
The archaeologists are suspicious of Philip but allow him to join them. As they start to uncover the secrets of le Bézu they find themselves in a race to make the information public before they are overwhelmed in a maelstrom of violence caused by the forces trying to stop them so that they can claim the treasures for their own illegal end