This 1928 NYPL overdue book slip was miraculously discovered in the 1980s during the construction of the Tenement Museum. The Museum kept the card on display, stating that the title of the book on the card is “one of the great mysteries, we unfortunately do not know.” That is, until yesterday, when the Museum turned to Twitter for help deciphering the handwriting. Within a few hours, the mystery was solved. The book, which may have never been returned, was Israel by by Ludwig Lewisohn. A great example of the power of social media.