The TARDIS arrives on an extinct volcanic island. Before long, the travellers are captured and taken into the depths of the Earth, where they find a hidden civilisation — the lost city of Atlantis.
| Actor | Role |
|---|---|
 Patrick TroughtonThe Doctor | The Doctor |
 Anneke WillsPolly | Polly |
 Michael CrazeBen Jackson | Ben Jackson |
 Frazer HinesJamie McCrimmon | Jamie McCrimmon |
 Joseph FürstZaroff | Zaroff |
 Colin JeavonsDamon | Damon |
 Noel JohnsonKing Thous | King Thous |
 Tom WatsonRamo | Ramo |
| PPeter StephensLolem | Lolem |
 Gerald TaylorDamon's Assistant | Damon's Assistant |
| CCatherine HoweAra | Ara |
| PP.G. StephensSean | Sean |
| PPaul AnilJacko | Jacko |
| RRoma WoodnuttNola | Nola |
 Graham AshleyOverseer | Overseer |
| TTony HandyZaroff's Guard | Zaroff's Guard |