Carcassonne 1942. A spirited and courageous young woman, Sandrine, finds herself drawn into the world of the Resistance in Carcassonne under German Occupation. Her network - codenamed 'Citadel' - is made up of ordinary women who risk everything to fight the sinister battles raging in the shadows around them.

As the war reaches its violent and bloody conclusion, Sandrine's fate is tied up with that of three very different men. But who is the real enemy? Who is the real threat? And who is the true guardian of the ancient secrets that for generations have drawn people to the foothills of the Pyrenean mountains?