Catherine Tate reprises her role as Donna Noble (previously seen in "The Runaway Bride") and joins the Doctor's side to foil an alien scheme involving weight-loss pills manufactured by Adipose Industries.
A visit to ancient Rome puts the Doctor and Donna in Pompeii just ahead of what the Doctor calls "Volcano Day," which is the eruption of Mount Vesuvius.
The Ood are encountered on the Ood Sphere, where the Doctor and Donna learn terrible things about the human race.
Freema Agyeman reprises her role as Martha Jones, who phones the Doctor as an army of the Time Lord's old enemies, the Sontarans, kick their diabolical plan into motion.
Poisonous gas threatens the people of Earth as the Sontarans attempt to convert the planet's atmosphere to suit their needs. Martha Jones: Freema Agyeman.
The TARDIS takes the Doctor, Martha and Donna to the planet Messaline, where the Doctor's DNA is used to create a daughter while a war rages between humans and the Hath. Jenny: Georgia Moffett.
Donna and the Doctor travel to 1926, where they meet the revered crime novelist Agatha Christie (Fenella Woolgar) and stumble into a murder mystery.
Mysterious shadows menace an abandoned library, the latest destination for Donna and the Doctor.
Donna loses her memory and leads a fast-paced life in a virtual world while the Doctor faces the Vashta Nerada with River Song, who reveals things about his future.
Vacation plans go awry for the Doctor when he joins tourists on a flight over the crystalline planet Midnight, where the passengers encounter a malevolent force.
The established timeline unravels after Donna meets a fortune teller, and Rose Tyler returns with dire warnings about Donna and the fate of the universe.
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