Series 4 (2008)
Episode title: The Poison SkyFeaturing: Tenth Doctor
Companions: Donna Noble, Martha Jones
First shown: 3rd May 2008
Related articles: Sontarans
Guide: This episode is the concluding part of a two part story, starting with the Sontaran Stratagem (series 4, episode 4).
The episode starts off with the cliff-hanger from the previous episode being resolved. Wilf is rescued by Donna's mother, Sylvia, when she smashes the car window with an axe, allowing him to escape. The Doctor and Donna return to the ATMOS factory to find that the Sontarans have taken it over.
Donna is told to go into the TARDIS, which she does, but then it gets stolen by the Sontaran's. The Doctor manages to communicate with Donna through code while he's speaking to the Sontarans, much in the same way he communicated with Mickey Smith in the Age of Steel (series 2 episode 6).
The Doctor also realises that Martha is a clone, and sets out to rectify that problem, while Luke Rattigan tries to get all of his students to go with him and the Sontarans to a new planet to start the human race again. They refuse and laugh at him, and when he informs the Sontarans they also laugh at him, and tell him that they would only have used his students for target practice. He escapes, just, but the Sontarans close off the teleport pads, while he lies sobbing in his mansion.
The Doctor, after freeing the real Martha, discovers that the Sontarans are turning Earth into a breeding planet, to breed many more Sontarans for war. The Doctor then goes to Rattigans mansion, and builds himself a weapon which clears the air of poisonous gas, and which can kill the Sontarans. He takes it on board their ship, after telling Rattigan to do something clever with his life, even though he himself is going to die defeating the Sontarans.
On board the Sontaran ship, the Doctor gives them a choice, which they refuse, and start their chanting of "Sontar-Ha!" Rattigan steps into the telepod, and is asked what he's doing, to which he replies "something clever" and teleports off to the Doctor, to take over, sending the Doctor back to Earth to Martha and Donna. Luke activates the weapon, killing the Sontarans and himself, but saving planet Earth.
The episode ends with Martha saying good-bye to the Doctor and Donna, when the TARDIS starts flying off without the Doctor flying it.
Also in this episode, you can see Rose Tyler on the TARDIS screen, but no one else bar the audience sees her.
This is the second of a two part story. Read the first part here.