Another merry riff on Washington power politics, struggles, and failures from the venerable curmudgeon and sage: an appealingly unholy marriage of Burr, Duluth, and a suavely Vidalian amalgam of Tom Sawyer and Tom Swift. In 1939, a 13-year-old prep school student who's identified only as ``T.'' (and who, we soon learn, is a ``teenage mathematical genius'') is yanked out of classes and driven to the title location's main building (``the Castle''), where, after meeting wax figures who come mischievously to life after the doors are closed to the public, he becomes a pivotal figure in crisscrossing plans to either avert or win a forthcoming world war. Specifically, undisclosed forces (among them may be James Smithson, the Institution's presiding genius) have determined that T., also, incidentally, ``the best schoolboy pitcher in the Washington, D.C., area,'' may possess knowledge that will enable his country to detonate a nuclear bomb without producing the ensuing chain reaction certain to destroy the world. After a disturbing first few hours within the Castle, during which he's declared ``prime veal'' and almost parboiled in the Early Indian Exhibit Room (then relieved--to his relief--of his virginity by a nonNative American ``Squaw''), T. settles sturdily down to business, reassuring a depressed-looking Abraham Lincoln and a truculently pacifist Charles Lindbergh, explaining to Robert Oppenheimer just where Einstein went wrong, and, thanks to a jury-rigged thermostat, traveling about in ``innumerable parallel pasts.'' Only a cad would give away the beguiling results of T.'s refreshingly ingenuous adventures and discoveries--not to mention the dozens of ingenious anachronistic gags with which the narrative is studded. This may be the wisest book that Vidal--this incomparably urbane observer of our revered past, debased present, and unpromising future--has even written. It is, as well, entertainment of the highest order. Even Norman Mailer will like this novel.