The first day of summer is the sea; the last is the moon.

Summertime. A family of three, a single father, Babis, and his twin children on the verge of adulthood, Konstantinos and Elsa, sail to the island of Poros on the family boat for their holidays. In the midst of swimming, sunbathing and making new friends, Konstantinos and Elsa meet unbeknownst to them, their birth mother Anna who abandoned them when they were babies. This encounter will stir up long-held feelings of resentment in Babis, resulting in a sun-kissed, bittersweet coming-of-age journey for everyone involved.