Summer 2002: 12-year-old Yuta, grieving for his father who died in a car accident a year ago, visits a place filled with memories. He meets a strange old man and travels back in time to 1977, to a village doomed by the construction of a huge dam.
Yuta meets a mysterious girl, Saeko, and makes friends with local boy Kenjo. The old man reappears and tells Yuta he will remain in the village for a month. It’s an unforgettable summer. But Saeko has a secret… The month passes, Yuta returns to 2002. Will he ever fully understand what he learnt in that summer?