Set in London during the Blitz, in occupied France and amid the rolling Chiltern hills of Buckinghamshire, this is the story of two cousins who, as squabbling rivals, are thrown together by the outbreak of war. Nell and Sylvie grow up quickly during the early days of rationing, black-outs, and the arrival of RAF planes in the skies over the Chilterns. Sylvie, marooned in England, is desperately worried for her parents who she left behind in Nazi-occupied Normandy, and puts up a barrier of bitterness to hide her distress. Nell, meanwhile, witnesses the crumbling of her parents' marriage. Even as the war rages on around them, the competition and jealousy between the cousins battles on - especially in romance. When the girls fall in love with the same man, the brave and unassuming RAF officer Alex Hammond, he is spared having to choose between them. The machinations of war change the course of all their lives, with devastating consequences. Sylvie continues to hurt those who love her and to hide her pain behind her tough facade. And for Nell, the only place she can ever find solace is inside the September Garden, the walled garden that her father tended so lovingly before he left. This is the only place she feels safe in, to where she is always drawn, and where she decides to hide her most dreadful secret...