After a long and unsuccessful struggle to get pregnant, Satoko and her husband decide to adopt a child. Over the next six years, the middle-class couple and their young son Asato settle into a comfortable, albeit routine, life. The family's orderly existence is shattered by the arrival of Hikari, a young woman claiming to be Asato's biological mother, demanding his return. As tensions mount, Satoko grows more and more emboldened to defend her family.