After the death of her father, 17-year-old Miranda Merchant reluctantly arrives on the shores of Selkie Island to live with her estranged mother, Amelia. As Miranda settles into island life, she finds herself torn between TJ, heir to one of the oldest Selkie families, and mysterious bad boy Leo who is part of the working-class "townies." When Miranda learns about the Seawalkers - who, according to local legend, are half-human and half-sea creature - she begins to believe that they could be real. As she uncovers more about her family's past, Miranda makes a startling discovery about her own connections to the Seawalkers.