Ben and Saoirse are two siblings who live in a lighthouse on a small island with their father. To protect them from the dangers of the sea, he sends them to live with their grandmother in the city. There, Ben discovers that his little sister is a Selkie, a sea fairy, who with her song can free the magical beings from the spell cast on them by the owl witch. On a fantastic journey, Ben and Saoirse will face fear and danger and fight against the witch to help the magical beings regain their power.