July 2003. After more than two years of suffocating plaster dust, thumping hammers, and hard-hat traffic jams at Nathaniel Rothschild's New York town house, 100 or so friends flock to the West Village for cocktails and exquisitely rendered canapés to see what Nat's done with the place. The furniture is shrink-wrapped in plastic and draped with drop cloths. Actually, the house isn't quite finished. If there were a theme to this party (and Nat likes to throw them), it would be "construction site." But the informal housewarming proves direly Promethean: Days later, some wires misbehave, and firemen are suddenly stampeding through the dining room, axes drawn. It would be two more years before Nat Rothschild would spend a single night here.

Nat's own tentacle of the Rothschild dynasty is generally suction-cupped to London, where the work engaging him most is investment in the former Soviet bloc and chumming around with Russia's power elite. At 34, Nat is part of a new business class who rarely spend more than four days in the same place—more frequent flier than jet-setter. A private plane makes the migrations to New York, Moscow, Switzerland, and Greece more tolerable.

(See the recent New York Times article on Rothschild.)

Somewhere in Nat's past, back when he was living in the States full time and managing a hedge fund, was a standard-issue Soho loft with ocean-liner columns and gymnasium floors. Also: a brief marriage. But there has been no call-the-caterer news for the future fifth Baron Rothschild of Tring. It is why, behind this brick facade in high Italianate style—a statement made in 1852 by some upwardly mobile merchant prince—there now exists a bachelor pad of such stirring modernity that it stands to redefine le goût Rothschild. The taste of the Rothschilds, inspiration in its day to America's edifice-envying robber barons and famously epitomized by Waddesdon Manor in Buckinghamshire. In 1988, Nat's father, Jacob, Baron Rothschild, inherited rights to occupy Waddesdon, commissioned by a bachelor Rothschild anticipating a roundelay of house parties but now owned by the National Trust. After the 1883 ribbon-cutting, Queen Victoria came to lunch. Her Majesty greatly admired the crested dormers and fanciful turrets of the approach, and ate poularde à l'Algerienne off the owner's Sèvres china.

Now restored to health, Nat's house seems a reaction to the Rothschild legacy of busy boiserie, porphyry vases, and Savonnerie carpets. He far prefers trigonometric edges, contemporary art—a Misrach here, a Pistoletto there, all hungry for acres of pristine white wall space. Instead of, say, a Gainsborough damsel in a plumaged bonnet, it is a shape-shifting Julian Opie stick figure (left) who, depending on the viewing angle, flashes her assets in the stairwell of this home on one of the city's most charming streets, where one might expect to see a hansom cab pulling up to the curb.

Nat's house was built and furnished with the kind of gentle understatement that wouldn't make him feel like he'd checked into a monastery. Who would introduce him to architect David Chipperfield but Nat's own father, past chairman of the historic-home-nurturing National Heritage Memorial Fund, the man who restored Spencer House to its former gilded glory? Which is not to say that Lord Rothschild has sclerotic ideas, this early acquirer of Giacometti who spent three years posing for a pair of portraits by London's cartographer of the flesh, Lucian Freud. For years, the banker-philanthropist has been the hurricane eye of all things cultural in London, a juror on the committee awarding architecture's highest honor, the Pritzker Prize. It was Lord Rothschild, after all, who engaged Robert Venturi to design a wing for London's National Gallery that was then compared by critic-in-a-crown Prince Charles to a "monstrous carbuncle on the face of a much-loved and-elegant friend." And now Nat would have his first go at being a patron, the eyes of his father's world telescoped on his progress.