Lupton forms an alliance with the spider to steal the Doctor's blue crystal, while Sarah and Mike attempt to alert people to what they've seen.
Quest roles:
Richard Franklin(Mike Yates), Nicholas Courtney(Brig. Lethbridge-Stewart), Terry Walsh(Doran (uncredited)), Pat Gorman(Pilot), John Levene(Sergeant Benton), Christopher Burgess(Professor Philips), Stuart Fell(Roga), John Dearth(Lupton), Carl Forgione(Land), John Kane(Tommy), Chubby Oates(Policeman), Michael Pinder(Hopkins), Kismet Delgado(Spider (voice)), Ysanne Churchman(Alpha Centauri (voice)), Terence Lodge(Orum), Andrew Staines(Captain)