Amidst abandoned houses and closed schools, ten-year-old Finn and his sister Cora while away their nights counting the few remaining fishing boats on the coast. Meanwhile Finn's music teacher, Mrs Callaghan, shares stories about his family, the island's ancient melodies, and its myths of mermaids and magic snakes. Then it's Cora's turn to vanish. Realising that he could lose his family as well as his home, Finn sets out to rescue his sister and bring life back to the barren waters.