A Treacherous Past — A.W. Lambert

A former Intelligence agent disappears and private detective, Theo Stern, is asked to investigate. A woman is found brutally killed, her neck viciously broken, and MI5 agents threaten Stern, warning him off the case. As an ex-London copper, Stern doesn't threaten easily, but when he is callously driven off the road and almost killed his resolve is tested to the extreme.