It's Thanksgiving and Hazel and Ned are back with their new-found family, including their father, for the holidays. Although their dad soon leaves for more international art fraud investigation, he leaves behind some notes for a treasure hunt, to amuse the siblings. In the course of solving the mysteries, Hazel and Ned make some discoveries of their own in the Frump castle on Isle du Loup, including an ancient diary and jewels. Soon they find themselves solving an old family mystery—is this what their father intended? And why do the notes suddenly turn more dangerous . . . ?
