UNIT is providing security cover at an experimental drilling project at Eastchester, designed to penetrate the Earth's crust and release a previously untapped source of energy. Soon, however, the drill head starts to leak an oily green liquid that transforms those who touch it into vicious primeval creatures with a craving for heat. The Doctor is accidentally transported "sideways in time" by the partially repaired TARDIS control console into a parallel universe where the drilling project is at a more advanced stage. Thwarted by his friends' ruthless alter egos, he works to save both universes.
Jon Pertwee
The Doctor
Caroline John
Liz Shaw / Section Leader Elizabeth Shaw
Nicholas Courtney
Brigadier Lethbridge-Stewart / Brigade Leader Lethbridge-Stewart
John Levene
Sergeant Benton / Platoon Under Leader Benton
Olaf Pooley
Professor Stahlman / Director Stahlman
Christopher Benjamin
Sir Keith Gold
Sheila Dunn
Petra Williams / Dr Petra Williams
Derek Newark
Greg Sutton
