The Poison Sky (TV story)

Synopsis
The Sontarans activate their masterplan, and begin to choke the whole of planet Earth. UNIT is left defenceless, with a traitor in their ranks. And as interplanetary war edges closer, 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
 * Colonel Mace - Rupert Holliday Evans
 * Luke Rattigan - Ryan Sampson
 * Newsreader - Kirsty Wark

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 a two part story that began with 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 habitable for themselves.

Rumours

 * A Rutan army will appear in flashback.
 * Details of the Brigadier's whereabouts are revealed.
 * The Sontarans steal the TARDIS.
 * UNIT will launch a nuclear strike. This is highly likely as the trailer for this episode is set around a countdown at [one of UNIT's bases. Also during the trailer Staal states that: "the planet is going nuclear".
 * 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

 * In the next time trailer, a corridor is seen exploding with Sontarans inside it. This is the same corridor that exploded in the Torchwood episode Sleeper. This is not a plot hole or error. It is common for TV shows to make use of sets more than once to save on the budget

DVD and other releases

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