During his lunch break on May 14, 1918, William T. Robey, a bank teller at Hibbs and Company in Washington D.C., traveled, as he often did, to the post office on New York Avenue. There, he hoped to purchase a new stamp celebrating the launch of the U.S. airmail service, set to make its first official flight the following day.

The stamp was an impressive sight. It featured a Curtiss JN-4 or “Jenny”, the same plane set to deliver the mail the following day, and was printed in carmine rose and deep blue. The striking color scheme no doubt wooed buyers, but like many of the avid collectors who gathered at post offices in Philadelphia, New York and the nation’s capital, Robey also knew that it enabled an even more spectacular possibility—a printing error. It was just the second time the Postal Service had attempted a two-color stamp and with the fervor of World War I, sloppy mistakes were a more likely occurrence.
Among the many philatelists, Robey was the lucky one. Instead of flying high through the skies, the Jenny on his stamp appeared upside down, as if it were doing an elaborate aerial flip for some grand barnstorming performance. Even luckier for Robey, the person selling him the stamps on that fateful day had never seen an airplane and couldn’t tell the difference.
When he saw the error, Robey saw opportunity, and he coolly asked to purchase a 100-count sheet for $24.
But when Robey asked for another sheet, the jig was up. In 1918, spending $24 on stamps was surprising, and $48, suspicious. The clerk closed down shop, and no one else would ever buy a sheet of Inverted Jennys.
Soon after, Robey sent word of the mistake to fellow friends and collectors, and it didn’t take long for the news to spread to postal inspectors, who were eager to reclaim the errant stamps. Of course, Robey rebuffed their offers, and for a few days, he hid the sheet of stamps under the mattress in a one-room apartment he shared with his wife. Under mounting scrutiny, he was eager to make a deal, and in a panic, he sold the stamps to Eugene Klein, a Philadelphia businessman an avid philatelist for $15,000.
The money allowed the Robeys to purchase a new house along with a car, which as the story goes, William promptly drove through the back wall of his garage. Its symbolic of a much larger blunder that emerged from his panicked selling: Robey assumed that more flawed stamps would emerge since they were typically printed on a larger 400-subject plate. But the other mistakes were caught and destroyed. Had Robey been patient, he could have made even more.
Klein, in turn, resold the Inverted Jennys for $20,000 to railroad scion Edward H.R. Green. Green divvied the sheet up into 25 rectangles of four Jennys apiece.

From there, the Jenny sets passed through various hands. Green almost burned some in a pub ashtray before fellow stamp collectors stayed his hand. He numbered the stamps in pencil, 1 to 100. One stamp was stolen from the New York Public Library; another Inverted Jenny possibly appeared on a 2006 absentee ballot.
About 98 of the 100 stamps, have been accounted for.
Thievery is responsible for those that are missing. In 1936, Ethel B. Stewart McCoy bought a quadruplet of Inverted Jennys. In 1955, she allowed the American Philatelic Society to display the stamps at a Virginia convention. That was the last time those four stamps appeared together, as they were filched from the premises.

Ms. McCoy’s foursome had been a gift in 1936 from her first husband, so its sentimental value to her greatly exceeded the $15,000 she insured it for before lending it to the American Philatelic Society to exhibit at its Norfolk, Va., convention in the fall of 1955.
Twenty years later, Chicago collectors found two of the four. But, after the early ’80s, there was no sign of the missing stamps, except, perhaps, on the ballot.
In April, however, everything changed. Another stamp had been found, having made its way across the Atlantic years before. An Irish man, Keelin O’Neill, knew he had a strange stamp among items he had inherited from his grandfather, but did not recognize its significance.
“I had no idea about the history and importance of the stamp until very recently,” he said to the Associated Press. When he tried to sell it to a U.S. auction house earlier this year, the assessor thought he had a forgery.
“The chances of him having the real McCoy, so to speak, were between slim and none,” George Eveleth, who evaluated O’Neill’s stamp, told NBC News. But when it turned out to be real, collectors tipped off the FBI.

During the World Stamp Show in New York City, the FBI handed it over to the American Philatelic Society. For his part, O’Neil turned out okay, scoring a $50,000 reward for his role in wrapping up a part of the mystery.
But the final Inverted Jenny remains at large, just as the question of who pilfered the block of four of the rare stamps, 60 years ago, remains unanswered.
The discoverer -Robey, continued to enjoy stamp collecting for another 31 years, he never owned another Inverted Jenny after selling the sheet to Klein. He continued to report other philatelic “discoveries,” but none were even remotely comparable to the Inverted Jenny. After witnessing the complete dispersal of Colonel Green’s holding of Inverted Jenny stamps, Robey passed away in February 1949.