Parts: 7
Writer: Malcolm Hulke
Airdates: 31 January 1970 - 14 March 1970
Production Code: BBB
Alternate Title: Doctor Who and the Silurians
Creature Feature: Silurians
Special Guests: UNIT (the Brigadier)
Story: UNIT is called in to investigate when an underground atomic research centre begins experiencing unexplained power losses and a higher-than-average rate of employee disturbances. The Doctor learns that the centre's logs have been tampered with, and that one of the junior technicians has returned from a spelunking trip with mental problems after his companion was killed. When the Doctor visits the hospitalized technician, he finds the man drawing cave-paintings on the wall of his room, his fear having tapped something deep in his subconscious.
The Doctor takes a trip down to the caves himself, and encounters a vicious dinosaur, but his life is spared when the creature is summoned away by some kind of signal. Curious, the Doctor brings the Brigadier and some of his men down to investigate. One of them sees a figure in the dark, and shoots at it. The wounded creature - a Silurian - makes its way to the surface, where it becomes the subject of a massive military search.
Beneath the surface, Silurians are being revived. Concerned about the state of affairs aboveground, they begin questioning the humans they are able to capture. The Silurians ruled the Earth millions of years ago, but were forced to go into hibernation...and now, having awoken later than they anticipated, they are ready to retake the planet. And if the apes currently inhabiting it must all be destroyed, then so be it. Only one thing stands in their way: the Doctor.