1956. Constable 'Thorny' Deepbriar is just a country bobby, but he's always longed to try his hand at detection. His chance comes when a young man is kidnapped, then turns up the next day, baffled but unharmed. With the affair dismissed as a joke, Deepbriar's unofficial investigation stalls when his only witness vanishes. Then some blood-stained clothing is found and somebody else goes missing. At last the CID takes an interest, and thanks to the flu epidemic decimating the force, Deepbriar finds himself at the very heart of a murder investigation. As the constable pulls all the strands of the affair together, a friend disappears and he has to risk his own life to prevent the murderer from claiming yet another victim.