IT is 1939. 'T', at 13, is more interested in baseball than his studies, school algebra being too 'dimwitted' for a boy of his mathematical genius. But the 'doodle' he pens in a moment of exam-room boredom not only fails him his algebra test - on the grounds that it has nothing to do with algebra - but also lands him a high-security research job at Washington's Smithsonian Institution. There, secret work on the atomic bomb - to say nothing of sex-tourism along the space-time continuum - is being conducted under the watchful eyes of Robert Oppenheimer, Albert Einstein and the institution's 18th-century founder James Smithson. The doodle, the product of his unusual ability to understand quantum physics by picturing the process on the baseball diamond of his mind's eye and then working out the numbers backwards, turns out to have been the formula for a theory of 'derelativity', building on Einstein's original E=MC2. And his high-minded, but drunken mathematics teacher, none other than Agent 35 of the Smithsonian's undercover network, has spotted its significance. However, the research on the bomb is only one of the Smithsonian's concerns. The institution is also experimenting with time, with the application of Einstein's and now T's theories. The schoolboy is also brought in to pleasure a former first lady of the United States, Mrs Grover Cleveland, who though 22 years old was last in the White House in the 1880s. Clearly, there is as much potential here for trashy melodrama and low farce as for moral philosophy, and Gore Vidal is not afraid to exploit it. T's first foray into time travel, for instance, lands him - with cavalier disregard for political correctness - among a band of Scotch-drinking, Bird's Eye-frozen-lima-bean eating, 17th-century Iroquois cannibals from the Early Indian Exhibit room. There he is promptly rescued from the cooking pot and seduced by the cradle-snatching Mrs Grover, cunningly disguised as a captive squaw. The front-cover, on the other hand, is so embarrassingly and garishly 'romantic', despite the mushroom cloud in the background, that only a dedicated follower of Mills and Boon would be seen dead reading the book in public. If the name Vidal makes you think of hairdressing salons, this cover will hardly dispel such unworthy associations. Yet there is none of this slush in the text. The Smithsonian Institution is not to be written off as Barbara Cartland meets The Hitch-hiker's Guide To The Galaxy, despite the satisfactorily silly romantic outcome and the burlesque parade of former (and alternative) presidents, first ladies, degenerate Iroquois and sex-crazed Eskimos who come to life after the public exhibits are closed. There is a serious point to this entertainment. The clouds of war are gathering over Europe, Vidal reminds us repeatedly, deliberately exploiting the best-known cliche of the period as a cynical leitmotif. Politicians and scientists talk in platitudes, as if their plans to develop a neutron-style bomb which will wipe out populations but leave the buildings intact are a victory for motherhood and apple-pie. But T sees the evil of what he is involved in. He experiments with time travel to avert both world wars, but only succeeds in preventing conflict in Europe. He can neither stop the nuclear attack on Japan nor his own death in it. The grisly details of the Japanese suicide attack which kills him recall not only Vidal's own experiences as a Pacific War veteran, but also remind us of the horrors of modern warfare. Yet Vidal never loses his sense of humour. With delicious irony, the dead presidents who authorised the Mexican War and the colonisation of the Philippines lecture Franklin Roosevelt on the dangers of becoming an imperial power. Meanwhile, General Douglas MacArthur, the victorious allied commander in the war against Japan, is condemned by T's meddling with time to a new role as an American Lord Haw-Haw, broadcasting calls to American troops to surrender to Emperor Hirohito. Yet the deft comedy and the zany plot only serve to underline the serious philosophical themes. With a light touch, and occasional lapses into irritating fatuousness, Vidal topples some of America's most treasured icons and subtly questions the ethical basis for its international supremacy. The Smithsonian Institution by Gore Vidal Little, Brown, $270