Part of the story takes place in 1916 Russia , involving the historical figure Rasputin.
The Doctor must survive a combined assault from her greatest enemies: the Daleks , the Cybermen , and the Master (played by Sacha Dhawan).
The special features the return of classic companions Tegan Jovanka (Janet Fielding) and Ace (Sophie Aldred), alongside modern-era allies like Kate Stewart and Vinder.
The episode was commissioned specifically to mark the BBC's 100th anniversary .