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 realises 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.

Who is attacking a speeding bullet train on the edges of a distant galaxy? Why are seismologists going missing from 21st century Earth? Who is defacing some of history’s most iconic paintings? Why is a Dalek trying to make contact with the Doctor? And just what hold does the mesmeric Rasputin have over Tsar Nicholas in 1916 Russia? In her last adventure, The Thirteenth Doctor must fight for her very existence, against her deadliest enemies: the Daleks, the Cybermen and her arch-nemesis, the Master.