The most valuable coin in the world sits in the lobby of the Federal Reserve Bank of New York in lower Manhattan. It’s Exhibit 18E, secured in a bulletproof glass case with an alarm system and an armed guard nearby. The 1933 Double Eagle, considered one of the rarest and most beautiful coins in America, has a face value of $20—and a market value of $7.6 million. It was among the last batch of gold coins ever minted by the U.S. government. The coins were never issued; most of the nearly 500,000 cast were melted down to bullion in 1937.
Most, but not all. Some of the coins slipped out of the Philadelphia Mint before then. No one knows for sure exactly how they got out or even how many got out. The U.S. Secret Service, responsible for protecting the nation’s currency, has been pursuing them for nearly 70 years, through 13 Administrations and 12 different directors. The investigation has spanned three continents and involved some of the most famous coin collectors in the world, a confidential informant, a playboy king, and a sting operation at the Waldorf Astoria in Manhattan. It has inspired two novels, two nonfiction books, and a television documentary. And much of it has centered around a coin dealer, dead since 1990, whose shop is still open in South Philadelphia, run by his 82-year-old daughter.
http://www.businessweek.com/magazine/gold-coins-the-mystery-of-the-double-eagle-08252011.html