After she loses both her husband and son in a matter of two months while she is ostracized from her community, a woman of the Sioux Nation calls upon the magic of her late grandmother to set things straight.

On a days-long fishing trip with her father and his crew, a 15-year-old girl learns her mother’s secret identity from a mermaid caught in the ship’s nets. After discovering the truth, she must fight to keep her and her sisters safe.