This is the first series to feature David Tennant as the tenth Doctor. He continues to travel with his companion Rose Tyler (Billie Piper), with whom he has grown increasingly attached. They also briefly travel with Rose's boyfriend Mickey Smith (Noel Clarke), and Camille Coduri reprises her role as Rose's mother Jackie. The series is connected by a loose story arc consisting of the recurring word "Torchwood". This is also the first series to be preceded by a Christmas special, which was commissioned to see how well the show could do at Christmas. The success of "The Christmas Invasion" led to the Christmas special becoming an annual tradition.

Arriving on the barren world of Androzani Minor, the Doctor and Peri find themselves embroiled in a long running, literal underground war. At the heart of the conflict is a substance called Spectrox - both valuable and deadly! The Doctor & Peri wind up being poisoned by the material, which is killing them slowly and painfully unless they can find a cure. As the conflict heats up and the situation gets more desperate, the Doctor realises time is running out - both for Peri and himself...

The TARDIS arrives on Androzani Minor, the source of a life-prolonging drug refined from a substance called spectrox. Production of the drug is controlled by Sharaz Jek, a facially deformed madman in self imposed exile, who blames Morgus, a powerful industrialist on Androzani Major, for all his misfortunes.
Jek is fighting government troops sent to liberate the drug. His weaponry is being supplied by gun-runners secretly employed by Morgus, who receives payment from Jek in refined spectrox. This gives Morgus a monopoly of the drug on Major.
Jek becomes infatuated with Peri, and saves her and the Doctor from being executed on Morgus's orders by government troops led by General Chellak. The two travellers escape after learning that they have contracted spectrox toxaemia, a fatal condition to which there is only one antidote - the milk from a queen bat, which the Doctor must obtain from the deep caves on Minor. Morgus, seeing his power base slipping away, travels to Minor.
In a climactic battle, Morgus, Jek and all the soldiers are killed. With moments to spare, the Doctor carries Peri back to the TARDIS, where he gives her all the milk that he has managed to collect. She recovers, but the Doctor has to regenerate to save his own life.

Adventures in time and space with the Tenth Doctor and his companion Donna Noble.

In a Mars base, the inhabitants are being infected by a mysterious water creature which takes over its victims. The Doctor is thrust into the middle of this catastrophe, knowing a larger one is waiting around the corner.

When the hospital she works at is transported to the moon, medical student Martha Jones joins forces with The Doctor to hunt down an alien fugitive before the oxygen runs out

The Tenth Doctor meets one of his previous incarnations.