Arriving on a desolate and windswept Earth the Doctor starts realigning the transmat refractors while Sarah and Harry go off to explore. Harry slips and falls into a pit and Sarah runs back to the Doctor to get help. The Doctor, however, has been captured by a trio of shipwrecked Galsec space travellers who were lured to Earth by a phoney distress call. Sarah, unable to find the Doctor, makes friends with a fourth space traveller, Roth, who tells her of the alien in the rocks who is experimenting on them.