In this, his fifth escapade, Inspector David Bliss goes undercover once again, and heads to St. Juan sur Mer on the Côtes d'Azur. His mission is so secret that even Bliss doesn't know why he is there: he only knows that he is tracking down a man the force wants in custody for an unstated reason.

But the winds of the Mediterranean provide clues that take Bliss off course and lead him to unravel two of the world's best known unsolved mysteries: the identity of the Man in the Iron Mask and the location of the stolen Nazi gold.