The Doctor and Clara save the frightened crew from a threat in an underwater base, but the Doctor questions the haunting.

An alien warlord sets a twisted plan in motion in order to ensure his survival on a remote Army outpost, and the Doctor may have to do something unthinkable.

In a Viking village, a girl named Ashildr is about to make a desperate mistake. The Mire are the deadliest mercenaries in the galaxy, famed for showing no mercy and Ashildr has just declared war on them. The Doctor and Clara have 12 hours to turn a peaceful village into strong fighters, ready for the deadly Mire.

England, 1651. The deadly Highwayman 'The Knightmare' and his sidekick stalk the dark streets of London. But when they find loot that's not of this world, they come face to face with The Doctor. Who is the Nightmare in league with? And can the Doctor avoid the hangman's noose and protect Earth from a devilish betrayal?

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.