Parts: 4
Writer: Geoffrey Orme
Airdates: 14 January 1967 - 4 February 1967
Production Code: GG

Doctor: second
Companions: Ben, Polly, Jamie

Megalomaniac of the Week: Professor Zaroff
Creature Feature: Fish People

Story: After landing on a deserted volcanic island, the TARDIS crew are captured, one by one, by unknown people hidden within a cave system. Even more surprising is that the cage within which they are kept prisoner turns out to be a lift...which starts to descend, very fast, causing all of them to lose consciousness.

When they recover, they find themselves in a colony of humans that are living deep underground. The TARDIS crew are served a sumptuous plankton banquet, but this questionably-luxurious treatment does not last long. They soon learn that they have stumbled into the lost continent of Atlantis, and if it ever was a scientifically-advanced nation, the residents have mostly lost such interests. Now they primarily worship the goddess Amdo, and the Atlanteans intend to feed the TARDIS crew to her fishy servants.

Fortunately, the Doctor realizes that a renowned scientist is living in Atlantis, and Zaroff's influence is enough to halt the sacrifice. And it is indeed fortunate for the Atlanteans that they did not sacrifice the Doctor - for Zaroff has a plan that he claims will raise Atlantis back above the surface of the water...but in reality, it will destroy the entire world...