A guy walks into a Swiss art dealer's gallery and admires a painting of a maiden done some time in the 19th century in Germany. He likes it enough to buy it for $19,000. The guy who buys it has some doubts. To him it doesn't look 19th century at all. It looks older and he begins to wonder just where it came from. So he sends it to a forensic art historian to get it tested. Modern science can peg a fake fairly easily using everything from electron microscopy to X-rays to carbon-14. So the art historian begins his work and then he notices a finger print set in the paint itself. This isn't unusual. Artists frequently smudge and blend with their fingers and lucky for the historian, this fingerprint is very clear. So he looks for known matches among many hundreds of paintings done by everyone from unknown art students to great masters. He finds a match. The match is so unlikely that he has other forensic art experts look at his results. They agree with him. The painting isn't 19th century and it isn't German. It's Italian. 15th century Italian. The fingerprint is that of Leonardo da Vinci. This forgotten 19th century German knock-off is now, officially, priceless. Estimates on its value begin at $150,000,000 but really, if it went to auction, it would be a once-in-a-lifetime opportunity and every billionaire on earth with any interest in art would likely send its price far higher. There are no known da Vinci paintings in private hands. There are books and drawings, a few rough studies, but no finished paintings. This is it: The holy grail of the art world: a lost da Vinci, in private hands.