A darkness arrives in the small town, Perdido, Alabama on Easter Sunday of 1919 creating an uneasiness that no one can quite figure out. Elinor Dammert is rescued in the aftermath of a flood by Oscar Caskey. She is beautiful and charming but her beauty hides a secret. Beneath the murky water of the Perdido River, she turns into a terrifying, creature that generations of Perdido residents thought was just