The Doctor takes Donna to his TARDIS and travels back billions of years to discover that an inert Racnoss ship became the core of the Earth as the planet formed around it; the Empress is now trying to wake her children aboard that ship with the huon particles. The Doctor and Donna return to the present as other Racnoss start emerging from the pit. The Empress uses her ship to start firing on Earth. The Doctor attempts to offer a peaceful solution but the Empress refuses, and the Doctor is then forced to remotely detonate explosive baubles used by the Santas at the walls of the base, flooding the pit with water from the Thames. The Doctor is prepared to die, but Donna urges him to escape with her, just as the Empress teleports to her ship to try to escape. However, this has weakened its defences, and the ship is destroyed by human forces under the direction of "Mr. Saxon". The Doctor offers Donna the opportunity to travel with him. She declines, but suggests he needs a companion to keep his temperament in check.