The Poison Sky (TV story)

Synopsis
UNIT is left defenceless, with a traitor in their ranks. And as interplanetary war edges closer, the Doctor has to fight to keep both Martha and Donna alive -- but will he have to make the ultimate sacrifice?

Plot
Under the command of General Staal, the Sontarans invade Earth. They fight UNIT, whose resistance is futile, and the Doctor finds out why the Sontarans need the artificial ATMOS gas from cars.

Cast

 * The Doctor - David Tennant
 * Donna Noble - Catherine Tate
 * Martha Jones - Freema Agyeman
 * Wilfred Mott - Bernard Cribbins
 * Sylvia Noble - Jacqueline King
 * General Staal - Christopher Ryan
 * Commander Skorr - Dan Starkey
 * Luke Rattigan - Ryan Sampson

Production crew
To be added

Story notes

 * Helen Raynor wrote this episode. Her Series 3 episodes Daleks in Manhattan and Evolution of the Daleks both occupied fourth and fith episode in the series. This two part episode also occupies episode four and five.
 * This is part two of The Sontaran Strategem.
 * This two partner is Douglas Mackinnon's first story as director.

Ratings
To be added

Myths
The sontarans need the gas from the cars to make the earth habitably from them.

Rumours

 * The poison sky may refer to the way the Sontarans are taking over the earth.This is false; it refers to the way the ATMOS gas in engulfing the sky, thus the Poison Sky
 * The Sontarans will clone Martha Jones, evidence from the trailers show Martha emerging from a green vat of water, and in The Sontaran Strategem preview a tank of the same green water can be seen as a cloning tank also in the cinema trailer Martha is seen covered in green slime. This has now been confirmed as true, but happened in the previous episode
 * the sontarans cannot breath are atmosphere because of global warming.
 * A Rutan army will appear in flashback.
 * Details of Brigadier Alistair Lethbridge Steward whereabouts are revealed.
 * The Sontarans steal the TARDIS.
 * UNIT will launch a nuclear strike.
 * The Valiant will be put to good use by Colonel Mace.
 * Donna will kill a Sontaran by the probic vent.

Filming locations
To be added

Continuity
To be added

Discontinuity, Plot Holes, Errors
To be added.

DVD and other releases

 * It will be released on the Series 4 boxset DVD in November 2008.