Worried about the Old Silurian's growing friendship with the Doctor, the Young Silurian has the scientist infect Baker with a virus and then release him.
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Norman Jones(Khrisong), Pat Gorman(Pilot), Peter Halliday(Soldier), Paul Darrow(Tekker), Geoffrey Palmer(Administrator), Dave Carter(Sergeant Duffy), Harry Swift(Private Robins), Peter Miles(Nyder), Thomasine Heiner(Miss Dawson), Nigel John(Young Silurian), Paul Barton(Silurian), Simon Cain(Silurian), John Churchill(Silurian)