Spring 1917. Under furious attack both from the ground and the air, the average survival time of a First World War reconnaissance pilot is eighteen hours. George Duckwell, reluctant novice-hero of the Royal Flying Corps, is living on borrowed time. Having joined up to escape disgrace at home, George can only watch in horror as a succession of comrades - inexperienced, under-trained and hopelessly idealistic - are shot down, burned, maimed and killed, while somehow he survives. Struggling to make sense of the conflict, George forms an awkward friendship with William 'Mac' MacBride, an enigmatic Canadian ace, waging his own private war against the legendary Red Baron. But when Mac falls for George's sweetheart - front-line nurse Emily - heartbroken George learns that Mac's mysterious past is darker than he imagined, and the fragile bond that keeps the two men alive comes under threat on the eve of the most lethal conflict the modern world has known.