Following a personal tragedy, Kate (Thandie Newton) and Martin (Cillian Murphy) try to repair their strained relationship by revisiting a remote island cottage where they were once happy. But their retreat proves more isolated than expected. The generator shorts out, radio signals prove increasingly erratic and the cracks in their relationship start to grow worse. Then one day an injured soldier (Jamie Bell) is washed ashore. He claims that a lethal airborne virus is devastating the outside world, and they must barricade themselves inside the cottage if they want to survive. But is he telling the truth...?