The parallel Inferno has broken through the Earth's crust, unleashing terrible seismic forces and dooming the planet. The Doctor hopes to return and save his world. But the bestial primords are closing in...
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Derek Newark(Greg Sutton), Pat Gorman(Pilot), John Levene(Sergeant Benton), Philip Ryan(Primord), Sheila Dunn(Petra Williams), Ian Fairbairn(Doctor Chester), Dave Carter(Roundhead Officer), Olaf Pooley(Professor Stahlman), Christopher Benjamin(Jago), Keith James(Patterson), Peter Thompson(Primord)