As the Twelfth Doctor nears regeneration, he stumbles on his first incarnation, also refusing to change. It takes a captain, a glass avatar and a familiar face to convince the Doctors the universe still needs them.
| Actor | Role |
|---|---|
 Peter CapaldiThe Doctor (12) | The Doctor (12) |
 David BradleyThe Doctor (1) | The Doctor (1) |
 Mark GatissThe Captain | The Captain |
 Pearl MackieBill Potts | Bill Potts |
 Nikki Amuka-BirdThe Glass Woman | The Glass Woman |
 Toby WhithouseGerman Soldier | German Soldier |
 Lily TraversPolly | Polly |
 Jared GarfieldBen | Ben |
 Jenna ColemanClara Oswald | Clara Oswald |
 Matt LucasNardole | Nardole |
 Nicholas BriggsDaleks (voice) | Daleks (voice) |
 Jodie WhittakerThe Doctor (13) | The Doctor (13) |
 William HartnellThe Doctor (1) (archive footage) | The Doctor (1) (archive footage) |
 Anneke WillsPolly (archive footage) | Polly (archive footage) |
 Michael CrazeBen (archive footage) | Ben (archive footage) |
 Patrick TroughtonThe Doctor (2) (archive footage) | The Doctor (2) (archive footage) |