Bride-to-be Donna mysteriously vanishes as she prepares to marry her boyfriend Lance in a glittering ceremony on Christmas Eve. She suddenly appears, to her complete astonishment, in the Tardis with the Doctor. As the Tardis races to get to the church on time, the Doctor and Donna are closely watched by the sinister figure of The Empress of Racnoss from her throne in her spaceship. It soon becomes clear that Donna is the key to an ancient alien plan to destroy the Earth.