In an oceanic world of floating villages, sea-forests and people who walk on water, timid boy Galeo's fear of disappointing his father has become the greatest obstacle in his life. When Galeo’s younger sister follows mysterious sea ghosts in search of their missing father, Galeo must leave the safety of home. Their journey brings them into conflict with pirates seeking control of the sacred water on which their community depends. Galeo’s practical inventions and growing trust in his sister offer a different path to bravery than the one his village has taught him.