November, 1940. Tom Tyler, Detective Inspector of the small Shropshire town of Whitchurch, is a troubled man. Only months earlier, he lost his soldier son, not in combat, but to a murderous enemy spy. His marriage is over and the love of his life is far away, doing dangerous undercover work for MI6. So he jumps at the opportunity to help out in the nearby city of Birmingham, where an explosion in a munitions factory has killed or injured many helping with the war effort. At first it appears like an accident, but when Detective Tyler investigates, a darker story emerges.