While Liz distributes the cure to the virus, the Doctor discovers the Silurians now plan to wipe out humanity by destroying the Van Allen Belt.
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Pat Gorman(Pilot), Peter Halliday(Soldier), Paul Darrow(Tekker), Dave Carter(Sergeant Duffy), Alan Mason(Corporal Nutting), Nigel John(Young Silurian), Paul Barton(Silurian), Simon Cain(Silurian), John Churchill(Silurian)