31 January 1970
Nicholas Courtney (Brigadier Lethbridge-Stewart), Fulton Mackay (Dr. Quinn) [1-3], Norman Jones (Major Baker) [1-5], Peter Miles (Dr. Lawrence) [1-6], Thomasine Heiner (Miss Dawson) [1-5], Ian Cunningham (Dr. Meredith) , Roy Branigan (Roberts) , John Newman (Spencer) , Bill Mathews (Davis) , Paul Darrow (Captain Hawkins) [2-7], Nancie Jackson (Doris Squire) , Gordon Richardson (Squire) , Pat Gorman [2-4], Paul Barton [4-5,7], Simon Cain [4-7], John Churchill [4-5,7], Dave Carter  (Silurians), Peter Halliday (Silurian Voices) [2,4-7], Geoffrey Palmer (Masters) [4-6], Richard Steele (Sergeant Hart) [4,6], Ian Talbot (Travis) , Dave Carter (Old Silurian) [4-5], Nigel Johns (Young Silurian) [4-7], Harry Swift (Private Robins) , Pat Gorman (Silurian Scientist) [5-7], Alan Mason (Corporal Nutting) [6-7], Derek Politt (Private Wright) , Brendan Barry (Hospital Doctor) .
|Written by||Malcolm Hulke|
|Directed by||Timothy Combe|
|Produced by||Barry Letts|
While caving in Derbyshire, two pot-holers are attacked by a huge creature and one is killed. At the nearby Wenley Moor nuclear research centre, which is built into the same caves, there are strange power losses threatening the reactor. Not only is everyone is at a loss to explain these incidents but there is also a high number of breakdowns involving staff members.
Now exiled to Earth and working for UNIT, the Doctor and his assistant Liz are sent for. As the surviving pot-holer begins to make cave-paintings in his ward the Doctor discovers not only a Tyrannosaurus Rex but a colony of Silurians – intelligent, walking lizards who have been dormant for millions of years. Now they have awoken to find that mankind has replaced them as the rulers of Earth – and they want it back. Can the Doctor find a way of thwarting their plans or will humanity be wiped out to usher in a new Age of the Lizards.
- The Silurians reappear in Warriors of the Deep, Bloodtide, Blood Heat, and The Hungry Earth/Cold Blood.
- In an alternate timeline created by the Meddling Monk (The Time Meddler), these events ended with the death of the Third Doctor At The hands of Silurian Morka, beginning a decline of Earth until the Seventh Doctor arrives in Blood Heat.
- They make their first appearance in the new series with Matt Smith