Francesca Bodin has a near-perfect life as an accomplished music teacher and professional flutist living in the Vermont countryside with her husband Ben, and their four-year old daughter, Addie. This ends suddenly when a snowmobiling accident traps the three of them in a frozen lake. Ben, after escaping onto the ice, leaves her and Addie to die.
Francesca believes she sees their dog pull Addie from the lake and drag her into the nearby woods. Desperate to help her daughter, she crawls from the icy waters and follows them. Once she enters the forest, however, she finds herself trapped in a sinister, dream-like world where night never ends, where Addie's whereabouts remain hidden from her, and where she encounters a group of women who, like Francesca, have been left to die and now seek to unleash their revenge on those who have harmed them. When they have Ben in their sights, Francesca realizes that if she is ever to escape this nightmare and save her daughter, she must first save the husband who abandoned them.
While Francesca's pilgrimage through this bleak landscape is on the surface a desperate attempt to find her daughter and reestablish her life as it was before the accident, it ultimately becomes an allegorical journey that takes her from despair to hope, from grief to acceptance, and from bitterness to forgiveness.