An incident in the skies over the Earth forces Clara to join Missy in a search for the Doctor, who has become convinced that he will not survive a final encounter with an enemy from his past.
The Doctor finds himself trapped alone inside the heart of the Dalek homeworld, with Davros enacting a final revenge at the end of his bitter life. Meanwhile Missy comes up with a wild plan for her and Clara to infiltrate the city.
After the discovery of an alien vessel deep under water, the Doctor and Clara arrive at a research base where the frightened crew are under attack from what appear to be ghosts.
The Doctor returns to the past where he must confront the alien warlord who is turning innocent victims into transmitters -- only to learn that the Doctor himself may have to die. In the future, Clara and the other survivors of the underwater outpost struggle to survive when it looks like there may be no way out.
The Doctor and Clara come to the aide of a Viking village under threat from the Mire, a race of alien warriors posing as their gods. But what will victory cost, and is it a price the Doctor is willing to pay?
When the Doctor arrives in seventeenth-century England he finds a familiar immortal playing the role of a highway thief. Though he agrees to help her steal an alien treasure, the Doctor has no idea that "the Knightmare" is secretly in league with a threat from another world.
The Earth faces all-out war with the Zygons after a rogue faction of the shape-shifting aliens kidnap Osgood and demand that the 20 million Zygons living in secret on Earth be allowed to live as who they really are.
With the shapeshifting Zygon rebels poised to force their own people to revert to their natural form all around the world, the Doctor must find a way to stop a war that appears inevitable. Meanwhile, Clara fights back against the Zygon leader who has taken her form.
Rigsy helps Clara and the Doctor locate a hidden safe haven for aliens inside the streets of London, where Clara puts her life on the line when she learns that her friend has been sentenced to death.
The Doctor finds himself trapped alone inside a castle on a world unlike any he has seen, where he is pursued by his own death and must stay alive long enough to solve the riddle of the Hybrid.
The Doctor's return to Gallifrey does not go as the President planned, as the Doctor defies all odds and travels to the end of the universe to try and save the life of someone close to him. But what he finds there may be the Hybrid prophesied to bring about the ruin of the Time Lords.
