The Doctor is avoiding Christmas when he is summoned to save a dying king. However, he soon discovers that the king's wife--River Song--has plans of her own. And she doesn't recognize the Doctor in his newest incarnation.
On modern-day Earth, planes freeze in the sky, locked in the time. UNIT turns to Clara for help, and they soon discover the person responsible: Missy, back from the dead. Missy wants their help on a unique quest: find the Doctor.
On Skaro, Davros asks the captive Doctor for one last favor before his death. Meanwhile, Clara and Missy attempt reenter the Dalek city.
The Doctor and Clara arrive on an underwater base in the year 2119, and discover a base under siege. Ghosts are haunting--and killing--the crew, and the Doctor sets out to determine what they want and where they come from.
The Doctor travels back to 1980 with Bennett and O'Donnell to try and stop the Fisher King from sending the message that dooms the base in the future. Meanwhile, in the future, Clara, Lunn, and Cass fight to survive the ghosts and discover that their enemies have expanded their ranks.
The Doctor and Clara are captured by 10th century Vikings, only to discover that alien warriors are abducting the village fighters and harvesting their adrenaline. A young woman challenges the aliens to war, and the remaining villages turn to the Doctor for help.
The Doctor travels to England 1651 to find an alien artifact. What he finds instead is an old acquaintance, who he must help answer an age-old question: who wants to live forever?
The Doctor and UNIT learn that the Zygon-Human truce has been broken, as a renegade faction of Zygons seek to conquer the world so that they can live in their true forms. Meanwhile, Clara witnesses a strange occurrence outside of her flat.
After the Presidential Airliner is destroyed, the Doctor and Osgood head back to London. Meanwhile, Clara discovers that she has been replaced, and the Zygon calling itself Bonnie sets out to recover the Osgood Box from the Black Archive.
The Doctor and Clara find themselves aboard the Le Verrier Space Station in orbit above Triton in the 38th century, and face a deadly threat that could consume all of humanity.
Rigsy wakes up one day and finds a tattoo on his neck counting down the minutes to zero. He calls Clara's emergency number for help, and the Doctor and Clara soon discover that Rigsy is bait in a trap... but it catches the wrong person.
The Doctor finds himself trapped and alone in an inescapable castle, stalked by an enemy that can't be fought. If he doesn't solve the puzzle of his captivity, then he will never leave.
The Doctor bargains with the Time Lords: his knowledge of the Hybrid in return for their saving Clara from death. However, the price may be far more than the Doctor is willing to pay.