Yuku, a little mouse, lives with her family in the underground depths of an old castle. She spends most of her time with her grandmother, who tells her various legends and mysterious stories, through which she teaches her wisdom and lessons. As her grandmother begins to fade and prepares for her final journey, Yuku finds in one of her books a remarkable story about a Himalayan flower that is able to bring eternal light. Yuku decides to leave the walls of her home for the first time, embark on an adventurous journey and bring the flower to her grandmother. Her journey is long and full of obstacles. However, thanks to her ukulele and songs, Yuku makes many friends who will help her along the way.