Happy: The Troll by The Yellow Door: Book 1, (Hardcover)

One day while Isabella, Tatyana, and their mom were walking through their New York City neighborhood, the family came across a yellow door by the side of some stairs. At five years old the girls, like all kids that age, had (and still have) an active imagination.

"Using your imagination, can you tell me a story about that door?" their mother asked. The girls nodded excitedly. Their mom leaned in to listen and the story of "Happy the Troll" was born.