After Sam rescues a troubled young girl in the woods, he brings her home to the ominous Osea Island, where inhabitants are preparing for a curious annual festival. As he meets secretive locals, Sam finds the island difficult to escape.

Plagued by a disturbing dream, Sam awakes to find himself in a compromising situation and misses the morning crossing to return to the mainland; after a series of confusing and terrifying events leaves him shaken, Sam quickly plots a way off Osea.

Sam learns the truth about his connection to Osea. Sam is in the fight of his life as he tries desperately to escape the islanders' clutches and make it back to the mainland in one piece.

Helen surprises her two daughters, Tallulah and Ellie, with a trip to Osea Island for Ellie's birthday; but the cottage she booked is suspiciously no longer available and cannot find a place to stay.

Helen reveals her true intentions in coming to Osea and is pressed on her past; a unique girl befriends Ellie and offers to take her to a mysterious place that is forbidden to outsiders.

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