The Poison Sky

The previous half of this two-part storyline saw Earth threatened by the war-crazy, potato-headed Sontaran (look out for much-transformed ex-Young Ones star Christopher Ryan as the alien chief) and their mysterious ATMOS devices.

As their masterplan for global death by poison gas is activated from under the bonnets of the planet’s cars, Martha’s UNIT (United Nations Intelligence Taskforce) organisation finds itself defenceless – with a traitor in the ranks.

Meanwhile, as interplanetary war edges closer, the Doctor realises that he will have to fight hard to save both Martha and Donna. But will he need to make the ultimate sacrifice to keep them alive?