The Doctor and Jo manage to escape from the mine with a maggot egg but Stevens is determined to stop them analysing it.
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Talfryn Thomas(Dave), Jerome Willis(Stevens), Stewart Bevan(Clifford Jones), Tony Adams(Elgin), Ben Howard(Hinks), John Rolfe(Fell), John Dearth(Lupton), Richard Beale(Minister of Ecology), Mitzi McKenzie(Nancy)