After 40 years of working at the expense of time with his family, Akio has finally retired, and to thank Eiko for continuing to support him, Taro, the husband of his daughter Fuyumi, has planned a "hot spring trip." Feeling excited about the family trip that Akio never got to take while he was still working, and feeling grateful to Taro, the group arrives at a hot spring resort. As soon as they arrive at the inn, Eiko and Fuyumi immediately soak in the hot spring. However, a man peers suspiciously at Eiko's body. Who is that man...?!