Since the end of the Great War, Inspector Ian Rutledge has fought to keep memories of the trenches at bay. Unable to sleep after his sister's wedding, he takes a short drive. Hours later he's far from London. The war, which he's kept rigorously in check all day, overwhelms him, and he has only a vague impression of the road unwinding before him. He's jolted out of his nightmare when his headlamps suddenly pick out a motorcar stopped in the middle of the road, and he narrowly misses it. Standing next to the vehicle is a woman, with blood on her hands and a dead man at her feet.

She swears she didn't kill Stephen Wentworth, telling Rutledge that a stranger stepped in front of their motorcar and without warning fired a single shot before vanishing. Rutledge persuades the Yard to give him the inquiry, but even he isn't sure whether he's seeking justice?or fleeing the emptiness that awaits him back in London.

Probing the victim's background, the Inspector uncovers conflicting views of the dead man. Wentworth appears to have been well liked by most people, yet his bitter family calls Wentworth a murderer. But who, exactly, did Wentworth kill? Is his death retribution for that crime? Or has his dinner partner lied?

When a second suspicious death occurs, the evidence suggests a dangerous predator on the loose, carefully stalking his victims. But where is he?