Wesley Theobald

Martha Jones summons the Doctor back to modern-day Earth, but an old enemy lies in wait. With the mysterious ATMOS devices spreading across the world, Donna discovers that even her own family is not safe from the alien threat - but is it too late to save them?

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, the Doctor has to fight to keep both Martha and Donna alive - but will he have to make the ultimate sacrifice?