Doctor Who: The Poison Sky

In BBC One's Doctor Who tonight, The Sontarans activate their masterplan, and begin to choke the whole of planet Earth.

UNIT is left defenceless, with a traitor in its 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?

David Tennant plays the Doctor and Catherine Tate plays his new companion Donna Noble.

Freema Agyeman plays Martha and Christopher Ryan also guest stars.

Doctor Who: The Poison Sky (series 4, episode 5/13), BBC One, Saturday 3 May 2008, 6.20pm.