One of the crew is the insane Taren Capel, who is using robots to carry out the murders. The Doctor discovers that there are also others who aren't what they appear to be either.
Quest roles:
David Collings(Poul), Pamela Salem(Toos), Russell Hunter(Uvanov), David Bailie(Dask), Gregory de Polnay(D.84), Miles Fothergill(S.V.7), Mark Blackwell Baker(Robot), John Bleasdale(Robot), Mark Cooper(Robot), Peter Langtry(Robot), Jeremy Ranchev(Robot), Richard Seager(Robot)