No one knows precisely what the nephew of a doctor said when he flung open the doors of his late relative’s garage to find a dust-covered siren of a car moldering in the darkness, though incredulously strewn expletives were surely involved.

The vehicle in question was a 1937 Bugatti Type 57S Atalante, one of fewer than 20 in existence, with a short but impressive genealogy that began with none other than Earl Howe, the first president of the British Racing Drivers’ Club. After trading hands a few times, the Bugatti—arguably one of the crown jewels of prewar automobiles—was purchased by Dr. Harold Carr in 1955. About five years later, the 57S went into his garage and never emerged. This mother of all barn finds recently sold at auction for nearly $5 million.

Regardless of the global economic climate, "when a car like this comes to market, collectors emerge," says James Knight, motoring department chief at Bonhams (www.bonhams.com), which handled the sale. "You accept that if you miss it this time, you’ll not get another chance in your collecting lifetime."

The Bugatti is in need of "preservation and conservation more than a restoration, as all the parts are there," says Knight. The new owner is a European collector who will entrust the car’s rebirth to an unnamed British restoration shop.

When the new owner previewed the car last fall, "he made a comment that shows how well dialed in he is," says Knight. "He said, ‘Jamie, whoever buys this car has a responsibility. A responsibility to do the right thing.’"