Winter. Helen surprises her two daughters, Tallulah and Ellie, with a trip to Osea Island for Ellie's birthday. After finding that the cottage she booked is suspiciously no longer available, Helen scours the island for a place to stay, but finds resistance at every turn.

As the islanders prepare for a fateful birth, Helen reveals her true intentions in coming to Osea and, after joining a search party, is pressed on her past. A peculiar girl befriends Ellie and offers to take her to a mysterious place closed off to outsiders.

Helen protects her family as tensions come to a dramatic conclusion.