Set against the backdrop of World War II in Nazi-occupied France, 'Citadel' by Kate Mosse unfolds the tale of Sandrine, a courageous nineteen-year-old involved in a French Resistance group called 'Citadel'. Comprising valorous women, the group not only engages in combat to free their homeland but also safeguards an enigmatic secret buried through the ages. Amidst betrayals and vanishing shadows, Sandrine's bond with Raoul, a fellow resistor, deepens. Yet, in tumultuous times where love and loyalty bear excruciating costs, these daring women confront the bleak realities of war, ready to defend their legacy at any price.