Sayumi is a married woman living an ordinary life with her husband and their university student son. One day, she accidentally leaves the bathroom unlocked and is seen by her son. Unaware of the incident at first, she doesn't think much of it—but her son begins to see her as a woman. On a hot, humid summer night, unable to resist the sight of his lightly dressed mother, the son finally pins her down. From that moment on, an abnormal relationship develops between mother and son, and an atmosphere far removed from normal family life begins to take hold.