Sia, an environmental activist, has a mother suffering from an incurable disease caused by environmental pollution. Sia, who is beloved by the entire nation for her touching speech on protecting the natural ecosystem at an international environmental organization, visits a mysterious arboretum filled with ancient trees with her mother, who doesn't have much time left to live. Sia has an experience as if she is greeting the spirit of nature there, hearing the sounds of the wind, trees, and birds. Drawn by the spirit's call, Sia discovers a mysterious stone inside an ancient tree...