The story of one of the most astonishing episodes of espionage and deception of World War Two.

This is the tale of two men: Claude Dansey, deputy head of MI6, and double agent Henri Dericourt, who was planted with the rival wartime secret service - SOE - at Dansey's instructions. From there began a terrifying trail of destruction.

After making contact with Dansey in 1942, Dericourt was recruited to SOE as the man desperately needed to organize top-secret flights in and out of occupied French territory. But at the same time Dericourt was in touch with German counter-espionage in Paris. As SOE congratulated themselves on a new asset, Dericourt gave the Nazis everything; every flight, operation and coded message he could.

Against a background of unprecedented deception and betrayal, Dansey's secret MI6 operation eventually led to the arrest of nearly one thousand men and women, hundreds of whom died in concentration camps.

How did it go so wrong?

A shocking, enthralling account of a devastating episode in the history of the British secret services, perfect for readers of Ben MacIntyre.