Ben Macintyre, an associate editor at the London Times, follows up his bestselling Agent Zigzag with another World War II spy story, Operation Mincemeat (Broadway, $15), a tale so wild and entertaining that it could be a James Bond caper.  Fictional agents and a bogus body are only part of the intricate plot by which MI5 successfully diverted Nazi intelligence from the planned Allied invasion of Sicily.  False documents baked in a cake, an undercover removal of a three-month-old dead body from a local morgue to stand in for a drowned corpse—one  clad in the thick underwear of an Oxford don—and an imaginary fiancée are only a few of the full complement of espionage tricks-of-the trade that Macintyre colorfully recounts.