Since its limited release just after the turn of the twentieth century, this American Tobacco cigarette card has beguiled and bedeviled collectors. First identified as valuable in the 1930s, when the whole notion of card collecting was still young, the T206 Wagner has remained the big score for collectors who have scoured card shows, flea markets, estate sales, and auctions for the portrait of baseball's greatest shortstop.

Only a few dozen T206 Wagners are known to still exist. Most, with their creases, stains, and dog-eared corners, look worn and tattered, like they've been around for almost a century. But one—The Card—appears to have defied the travails of time. Thanks to its sharp corners and its crisp portrait of Honus Wagner, The Card has become the most famous and desired baseball card in the world.

Over the decades, as The Card has changed hands, its value has skyrocketed. It was initially sold for $25,000 by a small card shop in a nondescript strip mall. Years later, hockey great Wayne Gretzky bought it at the venerable Sotheby's auction house for $451,000. Then, more recently, it sold for $1.27 million on eBay. Today worth over $2 million, it has transformed a sleepy hobby into a billion-dollar industry that is at times as lawless as the Wild West. The Card has made men wealthy, certainly, but it has also poisoned lifelong friendships and is fraught with controversy—from its uncertain origins and the persistent questions about its provenance to the possibility ...