This special is notable for its extensive fan service, bringing back numerous classic characters:

The episode follows the Thirteenth Doctor (Jodie Whittaker) as she faces her deadliest enemies—the Daleks, the Cybermen, and the Master—in a unified plot to destroy her legacy.

: With the help of past companions and a holographic AI of herself, the Doctor reverses the forced regeneration and defeats her enemies, but is mortally wounded by the Master in his final act of spite. Cast & Special Appearances

: During her forced regeneration, the Doctor encounters mental manifestations of past incarnations, including the First, Fifth, Sixth, Seventh, and Eighth Doctors.

: Disguised as Rasputin in 1916 Russia, the Master uses a captured energy being (a Qurunx) to fuel a "forced regeneration," successfully stealing the Doctor's body and identity for a time.

: Simultaneously, the Daleks attempt to trigger simultaneous volcanic eruptions across Earth, while CyberMasters attack UNIT headquarters.

: Tegan Jovanka (Janet Fielding) and Ace (Sophie Aldred) have central roles, while others like Ian Chesterton (William Russell) and Jo Jones (Katy Manning) appear in a final "companion support group".