London widow Cora Seaborne relocates to Essex to learn the truth about a rumored “sea dragon.” When a local girl goes missing, fears escalate.

Cora moves to Aldwinter, but the grieving villagers don’t welcome her. Naomi struggles with her guilt about what happened to Gracie.

After fishermen claim they were attacked by the serpent, Cora becomes more determined to understand what’s in the water.

Luke throws a birthday party for Cora. During an eventful night, Cora and Will get closer—and Luke notices Stella is hiding something.

Cora tries to put things behind her, but a chance encounter makes that complicated. Stella gets some bad news.

Luke processes the incident. Cora has a realization. Will struggles with Stella's illness.