L'Or de Rennes (The Gold of Rennes)

Context:

A pivotal book in the chain of influences behind The Da Vinci Code. Henry Lincoln read its paperback version while on holiday in the Cévennes in 1969, and it told him about the mystery of Rennes-le-Château and the priest Bérenger Saunière. The hosts reveal it was actually commissioned by Pierre Plantard, who fed Gérard de Sède the fabricated story about Merovingian parchments to support his own schemes.