While investigating a company that promises overnight weight loss with an easy pill, the Doctor is reunited with Donna, who has been searching for him in the hopes of joining him in his travels.
The Doctor and Donna arrive in Pompeii on the eve of the historic eruption of Mount Vesuvius, and must decide whether or not to warn the residents about the upcoming disaster.
Martha Jones summons the Doctor back to Earth, where U.N.I.T. is investigating a zero-emission car company that has been linked with suspicious deaths world-wide.
As the Sontarans launch their attack on Earth by unleashing poison gas into the atmosphere, the Doctor must deal with a missing TARDIS and a mole in his midst.
After the TARDIS pulls the Doctor, Donna, and Martha to a war-ravaged world, the human soldiers use a tissue sample to create a genetic offspring of the Doctor to join them in their unending fight.
The Doctor and Donna find themselves at a high society party in the 1920s, and must help the famous novelist Agatha Christie solve a real-life murder mystery.
The Doctor and Donna find the largest library in the universe empty, and a group of explorers led by a woman with an inexplicable familiarity with the Doctor.
As shadow parasites pick off members of the expedition, the Doctor and his mysterious friend race to save more than 4,000 souls. Donna finds herself living a perfect life, only to be told that it is not real.
Trapped with a group of tourists on the planet Midnight, the Doctor discovers that something is alive where nothing should be able to live -- and it's coming right for them.
Under the influence of an alien creature, Donna is thrust into an alternate life where she never met the Doctor -- and where the Doctor was not around to save the Earth.
