One day, the Sumikko friends find an old pop-up book in the basement of their favorite Sumikko Café. When they are looking at the book, the mechanism suddenly starts moving and the Sumikko friends are sucked into the book. In the world of the book, they meet a lonely Hiyoko, who doesn't where it is from or who it is. "Let's help Hiyoko find its home!" The Sumikko friends decide to help their new friend. The journey in the world of the book begins.