ONE WAS ALWAYS dimly aware of all those other Bonapartes: Joseph, the king of Naples, and Je'rom e, who married Betsy Patterson of Baltimore, and Louis, and Lucien, and the Beauharnais, Bernadottes and Murats. They kept turning up in footnotes or on the fringes of novels. Tolstoy knocks them in the very first line of War and Peace.

Here, in this short, sharp account, we see them as the millstones that finally sank Napoleon, outweighed only by Wellington and the Russian winter.

Joseph, who fancied himself a general, managed to lose Spain through outrageous incompetence and in 1814 failed to defend Paris for the tottering Emperor. Marshal Bernadotte, who had married Napoleon's old flame De'sire'e and had become crown prince of Sweden, betrayed him repeatedly and apparently assured the disaster in Russia.

"Had Sweden invaded Finland, which it had lost to the Tsar only in 1809, and threatened St. Petersburg," says Seward, "the war would have ended very differently. Napoleon later claimed that the city had been at the mercy 'of a small Swedish patrol.' "

Even Murat, the recklessly brave cavalry leader who had brilliantly saved more than one battle for Napoleon, went over to the Allies in the crunch, then "suddenly began to wonder if he was on the wrong side after all when he heard of Napoleon's string of victories . . ."

With precision, wit and remarkable clarity, the author chronicles the intertwined lives of these "half-savage squireens, scarcely more than peasants with coats of arms" through an all but unbelievable saga of vanity, stupidity and mindless greed. The effect is rather like Stoppard's mordant play, Rosencrantz and Guildenstern Are Dead, where we wallow in the petty ennui of minor characters while stupendous events are glimpsed in the wings.

With the first victories by the vastly energetic Napoleon, his family moved to Paris and started buying things: gold and jewels and a reputed 900 dresses a year for Josephine (even Marie Antoinette had quit at 170); two estates and a great town mansion for Murat, who later built a chateau and racked up an income of 1.5 million francs; diamonds by the handful and a gallery of paintings for Lucien; palaces for Louis, Je'ro me, sisters Elisa and Pauline, Bernadottes, Borgheses, Beauharnais and Napoleon's rapacious old black-bombazined skinflint of a mother, Letizia Bonaparte, known to all Europe as Madame Me're, the clan's reigning harpy.

Think of it: Napoleon, the Corsican Ogre, the Sourge of the World, the Antichrist, had a Mom.

They all clamored for huge salaries and grants, dipping up to the elbows into the treasuries of France. Murat managed to get awarded 100,000 francs for signing the death warrant of the Duc d'Enghien, scandalously executed on orders from Napoleon, who "was not a Corsican for nothing and saw the situation in terms of vendetta," Seward notes.

Then the First Consul crowned himself Emperor . . . and the family demanded whole countries for themselves. Fanatically loyal to his tribe, Napoleon handed out fiefdoms and titles right and left. Elisa became princess of Lucca and Piombino and grand duchess of Tuscany. The able Eug ene de Beauharnais, Napoleon's stepson, was made viceroy of Italy and his sister Hortense queen of Holland. Je'ro me turned himself into Girolamo, King of Westphalia, a crypto-kingdom that after the battle of Leipzig "vanished as though it had never been." ALL THROUGH Napoleon's career -- even after Elba, even after Waterloo -- these strutting, jumped-up refugees from a comic opera squabbled and whined and gave grotesque parties and paraded their little armies and generally acted out their fantasies. One begins to see Napoleon as the harried father in some cosmic sitcom.

On the other hand, as Seward makes clear, the emperor himself seems to have lost his head along the way. He never was much of a proletarian, putting down an early uprising in Paris with the famous "whiff of grapeshot." Even as first consul he started rolling back the gains of the Revolution, reinstating the church, restoring the trappings of royalty. He took to wearing a suit of red velvet, previously banned by the republic, and gradually brought back elaborate etiquette, "court dress, footstools for duchesses, so many horses for one's carriage" and more.

One of the most fascinating aspects of Bonaparte profligacy was sexual. The way those people jumped into bed was a caution. Seward retails it all with great verve, including some bits that couldn't go into a family newspaper. What a group!

A wonderfully readable book from a historian (The Bourbon Kings of France, The Hundred Years War) who wears his learning lightly.

Michael Kernan is a reporter for the Style section of The Washington Post.