Fiona, 10, is sent to live with her grandparents in a small fishing village in Donegal, Ireland, where they fish. Soon, she learns that an ancestor of hers married a Selkie, a seal who can change into a human. This is a myth in the area. Before her baby brother washed away and was never seen again, Fiona saw a naked little boy on the abandoned island of Roan Inish. When she saw him, she had to go and find out more about him.