The author introduces Mr. Post’s book of poems in a passing mention, among other things occurring simultaneously; at first, the volume is nothing more than “a slender leather-bound book” (41). Only once the Smithfork children learn the poems’ meanings and the history of New York City can they appreciate the value of the words Mr. Post intended to share with his children. Additionally, the book holds layers of puzzles. Not only do the poems guide the Smithforks, but the book also has other clues, such as the “long, stretched word, only recognizable to someone looking carefully at the exact right level” (64). The clues within the book lead to other clues, which lead to other clues.

At the heart of their hunt is this original poetry book, which serves as a motif for the theme of The Thrill of Solving Mysteries. Whenever the Smithforks and Eloise get stumped, they return to the source—the poetry book—to find what they missed. Though they struggle to decipher the clues as they go, Eloise finds new joy through the hunt itself. She tells the children, “I don’t feel that way,” when they ask if she believes the best times of her life have passed (259).