Élo and her parents spend their holiday at the seaside, as they do every summer. But this year, there are only sand and rocks where the sea should be. For months now, the sea has been receding, endlessly drawing away without visible cause. Elo does not fear this ebbing, unlike her mother, once a swimming champion, who now shuts herself away in their apartment. Despite the risks, Élo and her new friend Hugo try to swim.