In an imagined alternative 1944, after the fall of Russia and the failed D-Day landings, half of Britain is occupied Young farmer's wife Sarah Lewis wakes to find her husband has disappeared, along with all of the men from her remote Welsh village A German patrol arrives in the valley, the purpose of their mission a mystery Sarah begins a faltering acquaintance with the patrol's commanding officer, Albrecht, and it is to her that he reveals the purpose of his mission - to claim an extraordinary medieval art treasure that lies hidden in the valley But as the pressure of the war beyond presses in on this isolated community, this fragile state of harmony is increasingly threatened