Two Doctors stranded in a forbidding snowscape, refusing to face regeneration. A British army captain, seemingly destined to die in the First World War but taken from the trenches to play his part in the Doctor's story. In the final chapter of the Twelfth Doctor's epic adventure, he must face his past to decide his future. Along the way he realizes the resilience of humanity, discovering hope in his darkest frozen moment. It is the end of an era, but the Doctor's journey is only just beginning.