Sisters Rozenn and Dahut have grown estranged after the death of their mother Lady Malgven. Rozenn, the elder, has shirked court duties to care for animals on the moor, while her sister wields powerful magic to keep the kingdom from being swallowed up by the nearby sea. But as both daughters come to realize the harmful effects of the magic, they have to choose between their kingdom and unleashing hellish sea creatures kept at bay.