Princess Iris happens to notice a butterfly cocoon on the windowsill, and from then on begins a long journey of observing blue-spotted butterflies. Together with her companion Lark, she records their breeding and migration and exchanges research letters with a monk far away. As the greenhouse population gradually diverges through evolution, the two set out on a long journey to the alder grove and the southern slopes where the butterflies converge. Through seasons of tracking, she comes to understand natural evolution, grasps the deeper meaning of separation and connection, and writes her own field notes on life.
