Following the disastrous retreat of the British army from Dunkirk in 1940, England is plunged into a state of fear. The threat of a German invasion is real, and many German Nationals are interned in camps across the country. One such camp is on the ancient moor land of Prees Heath, near the small town of Whitchurch in Shropshire, where Tom Tyler is the sole detective inspector.
Young women from all walks of life have joined the Land Army, to help desperate farmers keep the country fed. When one of these young women is found murdered on a desolate country road, Tyler is almost glad for the challenge; he has been fretting for some time about the dullness of policing in a rural community. In addition, a former lover has reappeared and turned his emotions upside down; his soldier son seems utterly changed by his experience at Dunkirk; and his sixteen year old daughter is unhappy. As he pursues the murderer, Tyler finds himself drawn into an uneasy alliance with one of the Prees Heath internees, a psychiatrist, who claims to be an expert on the criminal mind.