Once again, Nancy faces two puzzling mysteries at once! The first concerns a valuable collection of rare books that Mrs. Horace Merriam commissioned anart dealer to sell—has he swindled her instead? The second mystery revolves around the baffling theft of a beautiful marble statue. To solve both mysteries, the famous young detective disguises herself and assumes a false identity. Despite these precautions, danger stalks Nancy's every move. An attempted kidnapping, a nearly disastrous sailboat collision, and an encounter with a dishonest sculptor are just a few of the exciting challenges that Nancy is faced with as she gathers evidence against a clever ring of art thieves.