Sarah Tucker, the protagonist of “Down Cemetery Road,” is a plucky, good-humored art restorer at the University of Oxford with a suburban house and a somewhat ineffectual bond-tradesman husband. As the story opens, a home in her neighborhood blows up in an apparent gas-main explosion. As Sarah begins to form suspicions about the blast’s origins, she becomes the classic Hitchcockian wrong man (so to speak), finding herself embroiled in a mystery that involves assassins and shadowy government agencies.