The Ark in Space (airdate November 20, 1983)
Intro: [cut off on available copy] ...ever overslept because your alarm didn't go off, you'll sympathize with the Earthlings on the Ark in Space. They have overslept for many years. But it really hasn't been their fault. No, the problem is a bug in their wake-up system. A very large bug. Manyvery large bugs.
"Next Week": Well, now that the Wirrn are no longer a problem, our suddenly-sentient space somnambulists can return to Earth. That is, if the transmat system works. Guess what. Can't guess? Then be with us next Sunday evening at 11, when the Doctor, Harry, and Sarah go down to a putatively deserted Earth to discover the problem, and find that... they are not alone.