Have you seen this painting?

At 1:24 a.m. on March 18, 1990, as St. Patrick's Day stragglers wobbled home for the night, a buzzer sounded inside the Isabella Stewart Gardner Museum in Boston. One of two hapless museum guards answered it, saw what he thought were two city policemen outside the Palace Road entrance, and opened the door on the biggest art theft in U.S. history.

After handcuffing the guards and disarming the museum's video cameras, the intruders, who had apparently stolen the uniforms, proceeded to take apart one of this country's finest private art collections. Painstakingly assembled by the flamboyant Boston socialite Isabella Gardner at the end of the 19th century, the collection had been housed since 1903 in the Venetian-style palazzo she built to display her treasures "for the education and enjoyment of the public forever."

But less than a century elapsed before Mrs. Gardner's high-minded plans for eternity began to crumble. During their 90-minute assault on the museum, the thieves managed to make off with three Rembrandts (including the Dutch master's only known seascape, Christ in the Storm on the Sea of Galilee), a much-loved oil by Johannes Vermeer titled The Concert, a Govaert Flinck landscape, a bronze Chinese beaker from the Shang era, five Degas drawings, the bronze eagle finial from a flag of Napoleon's Imperial Guard and a jaunty oil portrait of a man in a top hat, titled Chez Tortoni, by Edouard Manet. By some miracle, they left what is possibly the most valuable painting in the collection, Titian's Europa, untouched in its third-floor gallery.

Fifteen years later the case remains unsolved, despite wide-ranging probes by the Federal Bureau of Investigation, with assists from Scotland Yard, museum directors, friendly dealers, Japanese and French authorities, and a posse of private investigators; despite the Gardner Museum's promise of a $5 million reward; despite a coded message the museum flashed to an anonymous tipster through the financial pages of the Boston Globe; despite advice from psychics and informants; despite oceans of ink and miles of film devoted to the subject. It is as if the missing stash-now valued as high as $500 million-simply vanished into the chilly Boston night, swallowed up in the shadowy world of stolen art. Or has it?...