Cambridge, 1941. A teenage William Catesby leaves his studies to join the war effort. Parachuted into Occupied France as an SOE officer, he witnesses remarkable feats of bravery during the French Resistance.

Yet he is also privy to infighting and betrayal - some of the Maquisards are more concerned with controlling the peace than fighting the war. Double agents and informers abound, and with torture a certainty if he is taken, Catesby knows there is no one he can trust. Passed from safe house to safe house, with the Abwehr on his tail, he is drawn towards Lyon, a city of backstreets and blind alleys.

His mission is simple: thwart an act of treachery that could shape the future of France.