Yuriko (Kana Mochizuki) leaves her daughter in the care of a birch tree and heads overseas when her husband, Masayuki, is transferred to a developing country. However, a year later, she receives news that her daughter has fallen ill, and Yuriko returns to Japan earlier than her husband, only to fall into a trap and be taken to a remote island. There, she finds her younger sister, Miho (Mayu Yamaguchi), who was supposed to be working for an overseas company...