Josephine, not Napoleon, is the star of this absorbing ""Biography of a Marriage"" by the author or The Queen's Necklace, a historian who writes like a novelist and is as much at home in the Napoleonic era as in her own apartment. Born in Martinique, Josephine was married as a girl to the Viscount de Beauharnais, who treated her abominably and who died on the guillotine in the Terror; she herself escaped execution only by the fall of Robespiorro. Lovely, pliant, extravagant and charming, a woman with many lovers, in 1796 Josephine made a ""marriage of convenience"" with an importunate, sorawny young lieutenant on the make, Napoleon Bonaparte; four years later, finding she had married a genius, she fell in love with him. Nepoleon, notorious for his mistresses, loved her above all women, treating her children as his own and making her Empress of France, to the fury of her family; even after he divorced her because she could not bear him an heir he continued to love her. There is little of Nepoleon's military or political compaigns in the book, except as they effect his relationship to Josephine, but the era itself emerges sharp and clear, with its great figures clustered around the two protagonists, and around Malmaison and its gardens, Josephine's estate near Paris, where her charm still lingers. Brilliantly fashioned from letters and contemporary memoirs, this is a biography of exceptional calibre, equal to the enduring appeal of its subject.