Three years after discovering Poppel - the hidden village beneath New York City - and uncovering the truth behind the poem, 'Twas the Night Before Christmas, Maggie Ogden and Henry Livingston are once again reunited. The Foundling children are mysteriously vanishing from Poppel, and Maggie and Henry have been recruited to help in the search. However, Maggie not only wonders if she'll be able to get to the bottom of these disappearances, but she's...