London, 1918. Billy Prior is working for Intelligence in the Ministry of Munitions. But his private encounters with women and men - pacifists, objectors, homosexuals - conflict with his duties as a soldier, and it is not long before his sense of himself fragments and breaks down. Forced to consult the man who helped him before - army psychiatrist William Rivers - Prior must confront his inability to be the dutiful soldier his superiors wish him to be ...