The book, described by Dunn as "an epistolary lipogram," is a direct result of his work in the New York Public Library, and a huge fondness for words. The epistolary form -- a collection of letters -- is not that uncommon a literary device. A lipogram, a story written without the use of one or more letters, is a bit more rare. But at the library, Dunn found himself reading about lipograms and decided to challenge himself by writing one.