Series: 4

Original Air date: May 3, 2008

Number Doctor: 10th

Companion(s): Donna

Writer(s):   Helen Raynor

Director(s):  Douglas Mackinnon

Guest Stars
Christopher Ryan as General Staal
Rupert Holliday-Evans as Colonel Mace
Bridget Hodson as Captain Price
Dan Starkey as Commander Skorr
Bernard Cribbins as Wilfred Mott
Jacqueline King as Sylvia Noble
Ryan Sampson as Luke Rattigan
Christian Cooke as Ross Jenkins
Clive Standen as Private Harris
Wesley Theobald as Private Gray

Synopsis: The Sontarans launch the attack with their poison gas slowly encircling the Earth. They’ve also taken the TARDIS to its headquarters but don’t realize that Donna is inside. The Doctor realizes that the Sontarans have cloned Martha. He knows that fighting the Sontarans is of little use as they never surrender and are prepared to fight until they win. He decides to try and burn the poison gas that now encircles the Earth and with the help of the Sontarans teleportation system, send them a little surprise as well. At the end of it all, both Martha and Donna have to decide if they want to stay with the Doctor.

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