The first and fourth episodes of the second Doctor’s third story are missing. For the video release, they were replaced by a series of still photos appearing with the surviving audio.
The Doctor and his companions Ben, Jamie, and Polly are captured when the TARDIS lands on a deserted volcanic island, and their captors turn out to be survivors of Atlantis. The High Priest Lolem (Peter Stephens) decides to sacrifice them to the Great God Amdo. But the Doctor realizes that their last meal, made from plankton, must have been created by the brilliant Doctor Zaroff (Joseph Furst), who is long presumed dead. He is taken to Zaroff, who plans to raise Atlantis and thinks the Doctor can help him. But Polly is taken away for fish-conversion surgery, so she can breathe underwater, while Ben and Jamie are sent to the mines.
When the Doctor discovers this, he cuts off the power, which allows Polly to escape with the help of a young priestess named Ara (Catherine Howe). He also discovers that Zaroff’s plans will mean the end of the Earth. Ben and Jamie escape the mines and later they find Polly hiding in a temple. The Doctor tells a priest named Ramo (Tom Watson) what Zaroff means to do, and they inform King Thous of Atlantis (Noel Johnson), but the King does not at first believe them. The priest and the Doctor are to be sacrificed to Amdo, but Ben, who is hiding behind the altar, fakes the sonorous voice of Amdo and they escape. The Doctor sets out to cause a revolution--The Doctor seems to trigger revolutions wherever he turns up—with the help of the much-abused fish-people. The King fears the rebellion and begins to realize that Zaroff is quite mad. Zaroff shoots the King.
The Doctor finds the King bleeding and takes him to the temple for help. The walls of Atlantis begin to crumble thanks to Zaroff, and the city begins to flood. The Atlanteans are warned to get to higher levels, Zaroff drowns in his lab, and the time-travellers leave in the TARDIS.
The production of this strange story was problematic, not only because of script-changes, but because it was aired earlier than expected and Jamie had to be written in. Patrick Troughton and others were not pleased by the fish-people makeup, which was meant to be exotic but ended up weird and a little silly. The actors did their best to help with their fluid movements, but that enhanced the weirdness of it all. This was only Patrick Troughton’s third story, and he was still creating the Doctor. His loony nature was forced to bloom like an orchid with this bizarre story, and the only way he found to play against Furst’s over-the-top, crazy-as-a-loon mad scientist was to come up with a kind of clownish, bumbling Lieutenant Columbo-like brilliance, which became the trademark of the Second Doctor—a nice contrast between William Hartnell’s irascible old coot and Jon Pertwee’s Bond-like dandy.