After Philip's older sister and sole family member Helen marries, he goes off to live with his new step sister Lucy. He has trouble adjusting at first, thrown into a world different from his previous life and abandoned by his sister while she is on her honeymoon. To entertain himself he builds a giant model city from things around the house: game pieces, books, blocks, bowls, etc. Then through some magic he finds himself inside the city, and it is alive with the people he has populated it with.
Edith Nesbit (1858-1924) was the author of world famous books for children - the tales of fantastical adventures, journeys back in time and travel to magical worlds.