possibly the best library hoax

Jean Nepomucene Auguste Pichauld, Comte de Fortsas, was a man with a singular passion. He collected books of which only one copy was known to exist…. [W]hen he died on September 1, 1839 he possessed only fifty-two books, but each of them was absolutely unique. His heir, not sharing the old man’s passion for book collecting, arranged for an auction to sell off the library

Compelling no? The auction really happened, the rest of it is made up, the creation of a local antiquarian, having a bit of a practical joke. Read more at blacksundae, or see the auction catalog, itself a rarity, on Google Books.