In recent years, both Peter Dickinson (The Last House-Party) and Alan Scholefield (Point of Honour) have done beguiling, satisfying things with suspense tales in double-time: two interrelated plots--one past, one present--going on simultaneously, in alternating chapters. Here, however, Lord Denham (The Man Who Lost His Shadow) works hard at a similar concoction. . .but merely ends up with a plodding, teased-out treatment of a thin, contrived story of 1944 espionage and 1979 vengeance. In the chapters labeled ""Then,"" young viscount Derry Thyrde--soon to die in WW II combat, leaving his pregnant wife a widow--narrates a humdrum, vaguely Buchanesque sleuth-adventure: which one of Derry's dinner chums is the traitor (the implausibly clumsy traitor) who accidentally dropped secret, stolen D-Day plans under the dinner table? Derry and Wren officer Molly (his future bride) visit each of the rather colorless suspects (an earl, a leftwing M.P., a scientist, etc.); they find themselves in the usual sorts of peril; their romance blooms, padded out with a strained comic subplot about the refurbishing of Derry's old Rolls. And finally Derry and Molly do manage to foil the elusive spy's pro-Nazi plans, of course--though they don't ever determine for sure which fellow is the traitor. Meanwhile, ""Now,"" in every other chapter, Derry's son Derek, a young farmer/peer with money problems, finds himself framed for robbery. And who are the only other men who could have really committed this 1979 crime? The very same men who were the suspects in that 1944 spy-puzzle? (Or, in three cases, the sons of those 1944 dinner-mates.) So Derek, trying to clear his name by fingering the real culprit, parallels his father's sleuthing-trail. But it's only when Derek reads his father's long-buried narrative that he can identify the traitor/thief--the man who never forgave the Thyrde family for having sabotaged his dastardly schemes. Despite all the cute past/present connections: a far-fetched, skimpy notion, long-windedly belabored--with some mildly appealing sideshows (British wartime nostalgia, upper-class atmosphere) along the way.