Jamie McCrimmon, the newest crew member on the TARDIS, stands in awe looking round the ship's gleaming console room. While the Doctor busies himself at the controls, Ben and Polly watch over their new friend and try to ease his mind. They tell him that the TARDIS is a machine which has now taken him away from Scotland, but where (and when) they will end up is "in the lap of the gods". The Doctor tries to help out by quoting Scotland's poet laureate, Robert Burns, but realises too late that Burns is quite a bit later than Jamie's time. The lad is still none the wiser but seems to take all the strangeness in his stride.

The Doctor prepares everyone for landing. They all have their own hopes for their landing site, but Jamie is still wondering what on Earth he's gotten himself into. The ship lands smoothly and Jamie is in a hurry to go outside and see what is there. The Doctor waits until he checks the instruments and then opens the doors. They all go outside together.

The TARDIS has landed on a rocky beach. The roar of the waves is all around them. Polly jumps to the conclusion that it is Cornwall again, recalling the last time they landed on a beach, but she's only kidding. Jamie thinks it could be the rocky islands off the coast of Scotland, but the Doctor is sure that's not the case. The rocks are volcanic and not very old at all - only 25 million years. He points ahead of them to a volcanic cone that can be seen rising high above the island. Probably extinct. Everyone is in agreement that they would like to look around and so they head over the rocky ground toward the volcano. Perhaps they can get closer to the top and get a better look at the whole island.

The three young people get far ahead of the Doctor and out of sight of him on the slope. Polly is suddenly concerned when she sees movement down below them. She becomes scared and wants to go back, but Ben and Jamie want to keep going. Outvoted, Polly goes along. After some time, they've seen very little but Polly is getting tired. She doesn't want to go on. Jamie and Ben wish to continue so they leave her to rest outside a cave entrance. They promise to be back shortly.

Polly rests for a moment, looking around her. Among the rocks she finds a shard of pottery which she picks up to examine. Encouraged by what she sees, she goes inside the little cave mouth to look for more. But Polly is not alone in the cave.

Suddenly, Polly's scream rings through the air around the volcano. Ben and Jamie hear it and turn back quickly. They reach the cave mouth but see no sign of her. They are certain she's gone inside and plunge in to try and find her.

The Doctor, meanwhile, has returned to the beach and is examining pottery shards of his own. He thinks they are of Mediterranean origin but they don't seem very old at all. It is a mystery that he wishes to unravel.

Ben and Jamie enter the pitch black cave. They can barely see in front of them and must resort to calling out for Polly. There is no response and so they move deeper, feeling their way carefully. Suddenly, the same assailants who attacked Polly attack Ben and Jamie. They are helpless in the dark and are shoved into a sort of cage. It is lighter here and they can now see around them. They are surprised to see Polly nearby. She is unharmed and outside the cage, but is securely bound and cannot help them.

Before they can assess their predicament any further, the Doctor is shoved in to join them. None of them has seen their assailants, but at least they are all together and unharmed.

Without warning, the platform on which they are standing jerks to life and begins descending. It is a lift, moving very quickly. The Doctor unties Polly. The pressure change as they descend begins affecting them almost immediately and the lift continues to descend far below sea level. It becomes very hard to breathe and they all begin to feel woozy. The Doctor only has enough strength to tell them it's an oxygen deficiency before he succumbs to it. Polly opens the cage but soon she, Ben, and Jamie are also affected. All four of them black out. The lift continues its long journey downward.

Some time later, they all awake in another darkened chamber, unharmed. Ben recognises what happened to them as the fate of some deep sea divers. Blackout due to pressure change. He figures that they have arrived in a sort of compression chamber to help them acclimatize. They were brought here deliberately, but they are still stumped as to where "here" is. The Doctor thinks they may be dealing with cave-dwelling troglodytes and goes to consult his 500-year diary, but Polly seems very confident when she tells them they are somewhere near the year 1970. The Doctor asks for proof. Polly produces the shard of pottery she was looking at earlier and shows it to him. It is a faux Aztec piece that reads "Mexico Olympiad" on it. The Mexico Olympics were scheduled to take place in 1968, so they have arrived at some time after that. Jamie is of course confused by the entire conversation but takes it in his stride.

The group becomes aware of several men armed with tridents watching them. They don't look particularly hostile, but the Doctor and his friends know enough to proceed cautiously. Polly tries her limited range of languages to communicate with them, but they don't respond to French, German, or Spanish. Nor to Jamie's Gaelic. When the leader of the men gestures insistently with his trident, no translation is necessary. They must go with him.

The Doctor and his friends are led not into a cell, as they probably expected, but into a fairly ornate reception hall. They are left alone for the time being. The room appears to be carved out of the volcanic rock beneath the island, but it is comfortable and welcoming. In fact, a lavish buffet is spread out on a table before them.

Uncharacteristically, the Doctor attacks the food as if he hasn't eaten in some time. He deems it "ambrosia" and urges his companions to join in. He tells them it's plankton, which leaves Polly none the wiser. When Ben tells her it contains "little spidery animals", she refuses. Ben and Jamie are reluctant as well, even though the Doctor warns them there's likely little else down here to be had.

A group of men enter the reception hall. Most are guards, armed like the others with tridents. But they are led by an older man dressed in ceremonial robes. He is a high priest called Lolem and he addresses the visitors in English. Lolem tells them that he has been expecting them. The living goddess Amdo has foreseen their coming, saying they would "fall from the sky" in time for the festival of the vernal equinox.

Nervously, the Doctor inquires as to their part in the festival. Lolem regrets to inform them that their part is crucial and the Doctor is sure he knows what this means. Ben, Polly, and Jamie are grabbed by the guards and herded out, but the Doctor protests that he has something important to say. Lolem grants him 5 minutes to speak, then he will be forced to join his friends.

The Doctor says his information concerns a certain Professor Zaroff. Lolem's surprised reaction betrays the Professor's presence here, but he cannot understand how the Doctor knew this. The Doctor recognised the special plankton as Zaroff's work. He led the field in producing cheap food from the sea. The Doctor is impressed. He dashes off a note to Zaroff and asks Lolem to convey it. The priest refuses to be a messenger.

They are interrupted by a serving girl called Ara, come to clear the table. The Doctor urgently presses the message into her hand as Lolem drags him away. Ara doesn't understand why this stranger has chosen her, but something in his eyes compels her to help him.

Ben, Jamie and Polly have been taken to the Temple of Amdo, yet another chamber carved from the rock. It is very large and lit by torches, dominated by a giant fish-head statue on one wall. In the centre is a pool surrounded by four pallets. Sharks circle hungrily in the pool. The intentions of the worshippers of Amdo are quite clear. Polly is beginning to worry, but Jamie still hopes the clever Doctor can save them.

Ara hurries to Professor Zaroff's laboratory and tries to gain access. She seems somewhat frightened of being in this part of the city. She is refused entry but persists, asking the guard to see if Zaroff's assistant Damon will speak to her. She waits nervously.

Ben, Polly, and Jamie are forced onto three of the pallets with their heads toward the pool. They are all starting to worry now, knowing the Doctor is their only hope. But their hopes are dashed when Lolem brings him in. He is forced onto the fourth and final pallet.

Damon, a busy and impatient man, comes out to see Ara. He snatches the note from her and reads it quickly. He finally decides to show it to Zaroff, dragging Ara with him.

Chanting and music fill the temple as Lolem begins the ceremony. As the Doctor feared, he and his friends are to be sacrificed - by way of the sharks - to the goddess Amdo. Their pallets begin to tip upward toward the pool. The Doctor urges his companions to hold on for their lives.

In the lab, Damon presents the note to Zaroff. He is an older man in a white lab coat, his hair and eyes equally wild. If ever there were a true mad scientist, he would look like Professor Zaroff. Zaroff reads the note, his expression unfathomable.

The pallets have tipped even further and Polly can barely hang on. The sharks congregate below, as if sensing an impending meal. Suddenly Zaroff enters with several of his personal guards. He orders the ceremony to stop. There is clearly no love lost between Zaroff and Lolem and the priest refuses. But it is clear who holds the most sway. Zaroff insists on speaking to the Doctor.

The Doctor is released by the guards and he addresses Zaroff. However, he refuses to divulge the secret promised in his note unless his friends are freed. Zaroff considers a moment and then orders the others released. Clearly Zaroff cares only for his own work and his own interests. Lolem is furious of course and Zaroff's own guards must do the work. He orders Ben, Polly, and Jamie to be taken to the Labour Controller for work assignments. The high priest looks on with anger in his eyes.

The Doctor seems to know of Zaroff and his raging egomania. He begins by lavishly praising Zaroff's genius. Apparently, the Professor was reported kidnapped and killed 20 years earlier, causing a standoff between Eastern and Western blocs. (It seems clear that the Professor is of Eastern origin.) But the Doctor didn't believe this story at the time and says he is glad that the Professor is still alive. The flattery works and Zaroff relaxes. However, the Doctor is forced to admit he has no secret and Zaroff becomes angry again. But the Doctor insists that he is also a man of science and Zaroff has to admit he likes the Doctor's unorthodox style. He decides not to have the strange little man "torn to bits" by his guards and decides to take him to his laboratory to help him on his latest project.

The Doctor's companions are taken to the Labour Controller, who dispassionately sends Ben and Jamie down into the mine to work. Polly is held back. Ben and Jamie are concerned as to Polly's fate but they cannot stop themselves being dragged away. The Controller tells a worried Polly that "life is beautiful under the sea". Disquieting words that are unclear to her at first.

The Controller takes her to a gallery that overlooks a large water-filled grotto - the city's food production area. In the water, humanoid creatures swim. The Controller calls them farmers; they gather the special food that the inhabitants of this city eat. Polly is impressed. The creatures are quite beautiful, but she wonders how they can stay under the water for so long. The Controller explains that the creatures are given plastic gills through which they breathe. Looking closer, Polly can see that while the creatures are humanoid in general appearance, their heads are much more fish-like, including gills and fins. She is horrified, especially after she realises that these are regular humans who have been surgically altered to live like this. Aside from traditional slavery, there is this even more barbaric form of enslavement here. Polly is even more disturbed to find out that she is to become like that. She is to undergo the fish-conversion operation and become an undersea farmer!

In Zaroff's laboratory, the Doctor looks out through a viewing window into the sea. He is trying to work out where this underwater city is located. The egotistical Zaroff will not tell him but simply give clues to lead him to the answer. Finally the Doctor realises: Atlantis! The mythical kingdom is real, sunk beneath the ocean. He is amazed. The Doctor finds it surprising that Zaroff is accepted here, his "worship" of science in direct opposition to ancient temple ritual and idol worship, but Zaroff finds this the most appropriate place to "complete his work". He has gotten the Atlanteans to accept him and his battery of scientific equipment by offering them the greatest gift they could wish for: to raise Atlantis out of the sea.

Their conversation is interrupted by Ara. She is nervous and hurried, wishing to speak to the Doctor. She has discovered the plan to turn Polly into a fish person and has come to warn him. Thinking quickly, the Doctor formulates a plan but he needs to know where the city's main fuses are before he can do anything. Ara is of little help to him and so he sends her back to where Polly is and to watch over her and to wait for an opportunity to rescue her. The serving girl agrees and hurries off. The Doctor looks around desperately trying to find the equipment he needs while Zaroff bellows for him to join him elsewhere in the lab.

In the operating room, Polly is resisting the approach of Damon. He is to carry out the fish operation. He assures her it is quite painless but the hardness in his voice evokes no compassion at all. The struggling Polly is held down on the operating table by Damon's assistants as he prepares an anaesthetic injection. She continues to struggle and cry out but is no match for the assistants.

Back in Zaroff's lab, the Professor's interminable tour and lecture goes on. He is speaking about how life survived after Atlantis was submerged in the ocean, but the Doctor is not listening at all. He is fervently examining all of the instrument banks, looking for some way to help Polly. Zaroff of course is looking for fawning feedback, which the Doctor provides just to keep his attention diverted.

In the operating room, Damon is about to plunge the needle into Polly's arm when suddenly the lights dim. They stay down for a moment, then rise again. He starts again, but the lights go down and stay low. Furious, Damon aborts the procedure for the moment and stalks off to Zaroff's laboratory. He is certain that the Professor is behind this. Polly is left in the hands of his two assistants.

Zaroff is talking to his pet octopus in its tank, unaware that the Doctor is not beside him but rather standing beside the electrical controls. Damon bursts in, accusing Zaroff of draining off civilian electricity for his own energy-consuming project. It sounds like an old argument the two have had before. Zaroff can't understand what the fuss is about and goes to show him that he is mistaken. The Doctor has managed to step away from the panel in time to avoid suspicion. He watches the interplay interestedly, glad to know that Polly is safe while Damon is here. Zaroff shows Damon that there is nothing (currently) wrong with his electrical supply and blames the fault on the intake circuits at the clinic.

Damon persists, his voice rising. But Zaroff will take only so much. He becomes very angry, the fire showing in his eyes. He reminds Damon who educated him to his current level. It is Zaroff who taught him everything he knows. He assures his associate that he made him, and will break him if necessary.

In the darkened operating room, the minutes stretch on and the assistants are bored. One sends the other off to try and find some lighting equipment. Ara appears in the doorway and the second assistant, hoping to solve the problem for Damon, goes off to fetch some more fuses hoping that will be the answer. He leaves Ara in charge of Polly.

As soon as the men are gone, Ara grabs Polly and tells her to follow. She can see fine in the dark and will lead the way. Polly does not protest and the two women hurry off.

Meanwhile, Zaroff has discovered the Doctor's trickery and neither he nor Damon believe for a moment that it was an accident. Damon assures him Polly's operation will still go through, and Zaroff detains the Doctor "as his guest" to insure this.

Ara has led Polly along a narrow rock tunnel for what seems like miles. Polly is glad to be free but tired of running. It is still a bit further though; Ara is taking her to a secure hiding place.

Now alone with Zaroff, the Doctor tries to work out how he is allowed to continue his work in the face of such clear hostility from the Atlanteans. It must be in his promise to raise Atlantis from the sea: truly a "sugar-coated pill". But that is also something concerning the Doctor. He wishes to know how Zaroff can possibly hope to lift such a huge mass. Zaroff is only happy to explain, using a model of the city in a water tank.

He has already realised he can't lift the city, so he has decided to drain the water away, lowering its surface as he does for the model in the tank. Clearly there is no "drain" in the ocean, so his project is to create one... through the Earth's crust. He has found a deep fissure in the crust which renders the drilling depth only 15 miles. From there, the water can drain into the planet's core.

The Doctor is stunned at the mad scheme. If he succeeds, the water will drain into the white-hot core and be turned into superheated steam. The crust will crack and the planet will blow apart. All life will be destroyed! The Doctor watches in horror as Zaroff's eyes blaze with triumph. This is exactly his plan - to destroy the Earth. He will keep his promise to raise Atlantis from the sea... by blowing it into the sky! He wishes to do it for the mere achievement, the scientist's dream of supreme power. And, the Doctor knows, because he is utterly insane.

Jamie and Ben are brought to the mine workings by the Labour Controller. They are to start working very soon, joining another two men. One is a gabby Irishman called Sean, and the other is a dark and quiet foreigner called Jacko. The sounds of active mining equipment ring all through the area, making conversation difficult.

Suddenly the Controller forgets about the newcomers and addresses Sean and Jacko. He believes he has seen them concealing something between them. He searches them but finds nothing. Satisfied but wary, he sets them all to work and leaves.

Once alone, Jamie reveals what was hidden. A compass. Sean had managed to pass it to the lad just before he was searched and he explains that it is "as important as eyes down here". Clearly he and Jacko have an escape plan in the works. Ben and Jamie wish to join in and at first the two old hands are reluctant to allow them. They realise though that they are all in the same boat and must work together to get out. But first they must pretend to work to keep the guards happy.

Damon returns to the lab, still furious, to report that Polly has escaped. But Zaroff is busy and won't listen. The Doctor hears and is pleased. He tries to pump the surgeon for information, learning that shipwreck survivors are the main component of their workforce, miners and food-gathering fish people. To Damon, he is saving their lives and giving them useful work. To the Doctor it is old-fashioned slavery. He leads Damon over to a table full of test tubes, talking generally about the Professor and his plans to control the world. But it is only a ruse. He grabs one of the test tubes and quickly smashes it on the floor. A gas escapes, choking Damon. In the confusion, the Doctor runs for the door.

Ara has placed Polly in a hiding place. She is unsure where she is but feels safe. Ara however must return to her duties before her absence is noted. She promises to return when it is safe.

During a rest break, Ben, Jamie, Sean, and Jacko munch on plankton. Ben and Jamie are still wary of it, but Sean and Jacko are used to it by now. They warn the newcomers that the stuff doesn't keep and goes putrid within a few hours of harvesting. Talk turns to the escape plan, but Jacko is still wary of the newcomers. Sean is satisfied that they are not working for the Atlanteans and lets them in on the plan. While he was working one day, he came upon the entrance to an underground tunnel in the shaft. He's not sure where it leads, but both he and Jacko are willing to take the chance. They will either make it or fail in the attempt. They await only their chance to get back into that mine shaft.

That chance comes more quickly than they'd expected when a whistle blows and the miners are forced to line up. Extra labour is needed on another site. Ben and Jamie distract the Labour Controller as he chooses men, and Sean and Jacko sneak off into the mine shaft. Ben and Jamie are passed up for selection as they are too new, and when the group breaks up, they too head into the mine shaft. Jamie has managed to snag a light and he and Ben meet up with the others. They have not yet been missed and are now on their way to the underground tunnel. Jamie wonders what will happen if they are caught or forced to return because the shaft doesn't lead anywhere and Sean settles his mind. Runaway miners are killed on sight.

Damon has taken personal charge of the search for the Doctor. He and several guards scour the city, but they have had no luck so far. They run into Ara not far from the compression chamber, but she denies seeing any of the strangers. Not wanting to waste any more time with a mere serving girl, Damon and his men continue on.

From the shadows, the Doctor emerges, frightening Ara. He has been hiding here all along. He takes a moment to make certain that Polly is safe and sound and then asks Ara to take him to the Atlantean head of state.

Ara is taken aback by this request. Not only is she surprised at the audacity of the Doctor's request but also at her own acceptance. The Doctor is willing to take the risk of going to the council chamber and so is she.

They are startled by voices approaching and shrink back into the shadows. It is Damon again, speaking with another priest of the Temple of Amdo, a younger man called Ramo. Damon explains the situation to him, hoping he will help in the search. But Ramo is outspoken in his hatred for Zaroff, a callous outside with no respect for Atlantean tradition who appeals to all that is base in the people. He will do nothing to help Zaroff, even with the promise of Atlantis rising again from the sea.

The Doctor is encouraged by what he hears, thinking Ramo could be turned into an ally. But first he must get Damon away. Ara comes to the rescue yet again, leaving the safety of the shadows to tell Damon she has seen Polly down by the city market. Damon believes her and follows her there.

Before Ramo can turn to leave, the Doctor approaches him, explaining quickly that they are both on the same side. Ramo distrusts Zaroff out of instinct while the Doctor does so because of what he has learned. The Doctor can offer no real reason why Ramo should trust him, but nonetheless he does. He agrees to hear the Doctor out and they go to find a private place to talk.

So far so good for Ben and Jamie. The tunnel they're following has indeed led them to freedom in the caverns. If only they could find a way out. The group has come upon a fork in the tunnel and must decide what to do. Jamie suggests exploring a short way into each fork and meeting back at the crossing. All agree. Jamie and Jacko go one way, Ben and Sean the other.

The Doctor and Ramo find a quiet room in which to speak, lit by several fire pots. The Doctor explains that Zaroff's plan to raise Atlantis is really just a cover for destroying it. He assures a sceptical Ramo that it would be easy for Zaroff to do, demonstrating the effects of superheated steam using a firepot and a container of water. Zaroff will indeed raise Atlantis... in little pieces!

Ramo believes this, having always felt Zaroff to be a destroyer, and turns to the Doctor to stop him. The Doctor repeats his interest in speaking with Atlantis' ruler and Ramo agrees. He hurries off to see King Thous and try to gain an audience. The Doctor must wait and whistles a tune on his recorder to pass the time.

Ben and Sean have only gone a short way up their fork, chatting idly about the fate of people who have ended up here in Atlantis. Just like Sean and Jacko. Clearly no one has yet escaped to tell the tale of the sunken city. Suddenly Jacko is upon them, announcing that he and Jamie decided to go further than the agreed 50 paces as their fork looks promising. Jacko has come to let them know.

Ben still wishes to explore his fork a bit further and sends Jacko back to help Jamie. He and Sean will be back at the fork in 10 minutes.

Ramo has been successful in arranging a meeting, but they still must reach the council chambers unseen. The Doctor is kitted out in priestly robes like Ramo's and they set out. The Doctor seems to be quite enjoying himself... and the costume.

Jamie and Jacko's path has proved promising, but it is also quite dangerous. A chasm opens up between two parts of the tunnel and Jamie has rashly climbed down. As Ben and Sean join up with them, Jamie clings to the slippery rocks some 10 feet down. With a better view from above, Ben directs Jamie sideways to a better set of hand and footholds. With strength and skill, Jamie manoeuvres himself onto a safe foothold and to the next part of the tunnel.

All of them can breathe again.

Polly has been cooling her heels for some time in her little rock-walled room and she is quite bored. Going outside, she finds herself in the Temple of Amdo. The room in which she has been hiding is carved out behind the giant fish-faced idol.

Suddenly, Ben, Jamie, Sean, and Jacko emerge from the idol as well. Their escape tunnel has led to the room and out here. Ben and Jamie are very pleased to see Polly alive and well, although Ben can't resist poking fun at "the Duchess'" Atlantean clothing Ara has provided her. He is also amused at the story of her impending fish operation.

None of them has seen the Doctor since he met with Professor Zaroff. Ben wonders what he's up to.

Preparing to enter the King's chamber, the Doctor learns from Ramo that Thous believes Zaroff to be the deliverer of Atlantis. The Doctor knows he must tread carefully.

Luckily, King Thous has not been apprised of the arrival of the strangers and their subsequent escape. The King seems wise and imposing. The Doctor keeps quiet for the moment, at least until Ramo can properly introduce him and explain that they come on a matter of great urgency. Finally, the Doctor addresses the issue of Professor Zaroff. He begins by complementing Zaroff, saying he is a "worker of miracles". The King agrees.

But the Doctor draws the King's attention to Zaroff's eyes and the cold light in them. He even demonstrates the mad look the Professor gives when talking about his project. Bluntly, he tells King Thous that Atlantis' "deliverer" is mad as a hatter. Ramo's assertions that Zaroff is really working toward the destruction of Atlantis have a familiar ring for Thous and he is hard-pressed to believe them, especially when Lolem the high priest believes the project to be the answer to Amdo's prophecy.

But Thous is a wise ruler and agrees to ponder what he has been told. He sends them off so that he may decide whether to intervene in Zaroff's project. He will call them when he is ready.

Ara arrives in the temple with food for Polly. She is surprised to find five people now hiding in the temple. Polly asks why Ara has done so much to help them. She says that she hates Zaroff for enslaving and deceiving her people. She longs for the day when those who oppose him will rise up. She also says that she has seen the Doctor and will take them to him when it is safe.

They are alerted by noise from outside the temple that the priests are coming. They must get back into the little room behind the idol and hide for the time being. Ara cannot go with them or she will be missed.

Back in the King's chambers, the Doctor and Ramo are summoned back to Thous' presence. He says that he has given much thought to their words and has come to a decision. Suddenly Zaroff bursts into the chamber with his guards. Not the answer that the Doctor had hoped for.

Professor Zaroff takes the opportunity to taunt the Doctor as a "little man". The Doctor taunts right back, trying to get Zaroff to incriminate himself in front of Thous, but the Professor is shrewd. He says he made a mistake freeing the Doctor from the temple sacrifice in the first place and determines to return him to Lolem to pick up where he left off. The Doctor attempts to gain some mercy for Ramo, but the priest speaks out all on his own and is condemned to the same fate.

Thous is troubled by all of this and seeks reassurance from Zaroff, who of course tells him there is nothing wrong. He talks of his great plan to raise Atlantis from the sea, hoping to distract the simple-minded King, but this time he becomes quite swept up in his subject and is surprised to find Thous staring at his eyes. As the Doctor said, the King sees something different in Zaroff's eyes this time - a fire which disturbs him. But he brushes it off when Zaroff asks.

There is no time lost. The Doctor and Ramo are taken directly to the temple and made to kneel before two chopping blocks. Music and chanting begin again as Lolem intones the supplication. No sharks will be used this time. The executioner stands by, his sword at the ready.

Suddenly a piercing screech issues directly from the mouth of the statue of Amdo. A deep, distorted female voice issues forth, calling itself Amdo and ordering everyone present to bow so she may accept the sacrifices. Lolem and the others bow their heads as instructed. It is clear that this is not the first time their goddess has spoken. But the Doctor recognises the voice as something else: Polly. As he looks toward the fish-headed idol, he sees Ben leaning out from the secret room, beckoning him forward. With all the priests' heads bowed, the Doctor and Ramo are able to escape unseen.

Lolem finally looks up and believes a miracle has taken place. Amdo has eaten her victims! He is ecstatic.

The Doctor and Ramo are pleased to be alive and to see all these friends waiting for them in the little room. Polly shows off the electronic microphone system she used to impersonate Amdo. It has clearly been there for years. Sadly, Ramo realises that any time Amdo spoke in the past, it was a trick. He is crushed. The Doctor, meanwhile, gets acquainted with Sean and Jacko.

Zaroff has taken some time to reassure Thous of the impending success of his plans. He will be ready to raise Atlantis in two days' time. This news seems to quell Thous' earlier concerns and he is more than prepared for this miracle to take place. He plans to order special prayers for all his people. The conference is disrupted when Lolem bursts in past the guards, extolling the other miracle that has just happened in the temple.

At first Zaroff is pleased, thinking that the only obstacle to his plan is now gone. But when he learns that the Doctor and Ramo "disappeared" before they could be beheaded, he becomes furious, calling Lolem a liar and denigrating both Amdo and Lolem's faith. Thous tries to keep peace, choosing to believe his priest and gently admonishing Zaroff for questioning the faithful.

But Zaroff will not be quelled. He clearly fears the Doctor and orders a search of the whole of Atlantis for him. He will brook no opposition from the King and will not bow to his faith. Faced with the loss of his great dream to see Atlantis rise again, Thous relents and says that the guards will obey Zaroff. However, there is a deep sadness in Thous' voice. Something in him has died just now.

Meanwhile, the Doctor and his friends discuss their next move. He is certain they must attack Zaroff directly in order to stop his mad scheme to destroy the world. The first step is to cut off Atlantis' food supply. The seafood that everyone lives on cannot be stored and goes bad a few hours after harvesting. By starving the people, chaos will erupt and Zaroff will have his hands full, making him vulnerable.

In order to stop the flow of food, they must convince the fish people to go on strike. Seeing as they have been surgically altered and enslaved into their current position, the Doctor thinks it could be easily done. Sean agrees and the Doctor assigns the task to him. His Irish gift of gab makes him ideal. He decides to take Jacko with him. Meanwhile, the Doctor and the others have another task to perform - kidnap Professor Zaroff!

Some time later, the Doctor's sketchy plan is in motion. He is disguised as some sort of pirate/gypsy with cloak, bandana, and sunglasses. He is seated at the edge of a salt-water fountain in the centre of the market place with a tray of baubles as if he is a merchant. Music and noise abound in the market, children play and the stalls are busy. The Doctor is hardly noticed as he tootles on his recorder. Neither are Polly and Ara, identically dressed as everyday

Atlanteans and cruising the market place.

The three of them have been waiting for Zaroff, certain he will be arriving at the market soon in his sweep on Atlantis. But something has gone wrong. Two guards appear, searching the market for the fugitives, but Zaroff is not with them. Clearly the Professor is being cautious.

Polly is worried about being spotted by the guards and so Ara grabs her and takes her to the nearby stall of a carpet seller. The woman, called Nola, is a friend of Ara's and agrees to help with no questions asked. Polly is bundled beneath a carpet and Ara sits on it just as the guards arrive.

The arrogant guards badger Nola and then take their tridents to poke at the carpets. Nola becomes indignant, accusing them of trying to ruin her wares. They finally relent and walk away, laughing. Polly is safe... for the moment. But it was a close call.

Suddenly Ben and Jamie appeared, dressed as guards, announcing that Zaroff is on his way. They pretend to be interrogating the Doctor as the two guards pass by, successfully shielding themselves and the Doctor from them. Once they are past, Ben and Jamie get into position. Their task: to separate the guards from Zaroff.

Zaroff appears, his eyes ablaze, scanning the teeming market place. He badgers Ara, who pleads ignorance, and then moves on. As hoped, Zaroff sends the real guards off to another part of the market and directs two others standing nearby to come with him. He is pointing to Ben and Jamie.

Suddenly the Doctor leaps up and calls out to Zaroff. Chaos ensues with the Doctor leaping and shouting, leading Zaroff and his guards on a merry chase. But his "guards" are Ben and Jamie, who allow the Doctor to escape (as planned) into a nearby tunnel and then follow Zaroff in pursuit. Polly waits in the tunnel to "direct" Zaroff, making sure her face is not seen. Soon, she, Ben, and Jamie pursue the Professor as he pursues the Doctor.

The Doctor races to the temple where Ramo awaits. He has shed his disguise and has only a moment to hide himself before Zaroff arrives. The Professor orders his guards to capture Ramo and Ben and Jamie pretend to do so for the moment. He then finds the Doctor waiting in the shadows, apparently trapped. He moves in for the capture but the Doctor blows dust into his eyes from his recorder. Zaroff staggers back and Ben and Jamie grab him. Zaroff is now their prisoner and they drag him to the secret room behind the idol as Polly joins them.

Sean and Jacko have gone to the food production area and gathered a group of fish people together. They hang above the water, listening to the man. His strategy is to get them all fired up; he does so by taunting them! Before long, they are all chattering angrily and tossing seafood at him. Once he has their attention, he tries to sell them on starving Atlantis, offering them the prospect of freedom if they succeed. After a moment of thought, they all agree.

The fish people begin their blockade immediately, swimming far and wide to pass the word to their comrades.

In the secret room, Professor Zaroff seems quite jovial despite the seeming setback of his capture. He announces that they are all too late - his nuclear reactor has already been activated and the process of destruction will happen with or without him. The Doctor refuses to believe this, figuring the arrogant Zaroff would have to be present to complete the destruction personally. He would never plan to "miss his big moment".

Zaroff turns to threats, railing against the pathetic fools who would try to stop him. But suddenly he trails off and seems to fall into a seizure, collapsing back and clutching his chest. All are concerned. The Doctor helps him to a resting place.

Jamie thinks Zaroff is faking and the Doctor can't confirm or deny. Either way, Ben is sure they've put paid to Zaroff's scheme. But the Doctor is concerned, fearing that there still may be danger for Atlantis. He decides to get to the laboratory and check things out for himself. Ben and Jamie will go with him while Polly and Ramo stay and look after Zaroff.

The three men emerge into the temple only to find a group of worshippers coming in. They must hide and wait until the others are gone before they can escape, ducking behind a wall near the shark pit where they will not be seen.

Back in the secret room, Polly looks over the fallen Zaroff resting in the corner, and she thinks he doesn't look so evil now. Ramo disagrees. He is well acquainted with Zaroff's evil and assures the scientist that he will pay for what he has done. Weakly Zaroff asks Ramo for pity. He wishes Ramo's help in praying to Amdo for atonement. With Polly's encouragement, Ramo agrees and goes to help the stricken Zaroff up.

In a second, Zaroff's weakness is thrown off and he is as strong as ever. Jamie was right; it was all a ruse. Zaroff throttles Ramo and knocks him to the ground.

Almost crazed, Zaroff looks around and finds a weapon - a spear. He moves toward the helpless Ramo, moving in for the kill. Polly leaps on Zaroff to try and stop him, but he tosses her away and plunges the spear into Ramo. Polly screams.

Zaroff then grabs a nearby sword as well as the cowering girl and forces her out of the room. He is feeling invincible now.

Out in the temple, the worshippers are finally gone and the Doctor, Ben, and Jamie can move freely. However, the Doctor realises they'll need a guide to reach the laboratory from here. He sends Jamie back to the secret room to change places with Ramo, but Ramo is already on his way out, staggering and ashen.

The three men help Ramo down and make him comfortable. It is clear to them what has happened and who is responsible. Jamie takes a look in the secret room and finds Polly and Zaroff gone. He has taken her as a hostage. Jamie must go after them while the Doctor and Ben go on their own mission.

Zaroff has taken the time to tie Polly's hands and he is now dragging her by the end of the rope along a narrow rocky tunnel. Polly is protesting all the way, Zaroff countering with threats. Suddenly, Jamie appears to confront Zaroff.

Zaroff attacks Jamie with his sword, forcing the lad to bob, weave, and leap to avoid being cut to pieces. Polly jumps on Zaroff and ends his assault, but Jamie still can't get the better of him. In the end, Zaroff shoves Polly at Jamie and runs off down the tunnel laughing madly.

Polly and Jamie decide not to pursue him, but to try to get back to the laboratory before him and warn the Doctor. They, too, need a guide. They must find Ara.

In the King's chamber, Damon reports the fish people's revolt to Thous. He is heartsick, wondering why his people are acting like this. But Thous is no longer in control. The fish people are Zaroff's creation and he should be here to deal with the crisis. Damon tells him that Zaroff has disappeared. With a heavy heart, Thous sends Damon off to hear the grievances of the people, while he himself prays to Amdo for support.

Suddenly Zaroff bursts in, followed by two guards. He is clearly aware of the revolt and assures the King that his guards will restore order. Those who resist will be killed. Thous is stunned and tries to regain some measure of control over Atlantis from the arrogant Zaroff, but it is now far too late. The madman is in control and Thous himself has given him that power pursuing the dream of raising Atlantis from the sea. And now the King realises the Doctor was right all along - Zaroff's promises were empty.

Thous orders Zaroff's project stopped immediately. Zaroff mocks the King and his futile attempt to take power now, and when Thous tries again to demand the scientist's cooperation, Zaroff laughs in his face.

Zaroff pulls out a gun and callously shoots Thous down. He orders his guards to shoot the King's guards and as the shots ring out, Zaroff's eyes go steely cold.

On their way to the laboratory, the Doctor and Ben decide to stop by the council chamber for one final attempt to enlist King Thous' aid. They arrive to find the chamber empty and Thous on the floor. He is still alive but bleeding from the bullet wound. The Doctor thinks he'll be all right as no vital organs appear to be damaged. But they must get him to safety just in case. Then they must stop Zaroff.

They head for the secret chamber in the temple. There Thous will be safe. They find Sean, Jacko, and Ara there to look after the injured King. The Doctor learns that Polly and Jamie have gone to the lab in search of him, following Ara's directions. The Doctor hopes to find them along the way, as he has a new plan to stop Zaroff that will prove dangerous to them all.

He has decided the only way to stop Zaroff is to flood the laboratory and render the equipment useless. He plans to accelerate the power on the reactor and break down the sea wall, letting in water. The problem is that this will flood the entire lower portion of Atlantis, the temple and tunnels included. Everyone must be warned and moved to higher ground - a task which the Doctor assigns to Sean and Jacko. He and Ben will head to a generating station to put the plan in motion. Only one question remains: can they all swim?

In his laboratory, Professor Zaroff is making final preparations for breaking through the Earth's crust. Once that is done - in a mere 15 minutes' time - the ocean will drain into the core and become super heated steam, blowing the planet apart. The mad scientist can hardly wait.

However, there is one snag. One of his reactor stations is reported as unmanned. The technicians, starving due to the fish people's strike, have abandoned their posts in search of food. Zaroff angrily orders his guards to replace them, knowing that none of this will matter in a short time. Still he is angered by the delay.

On their way to the generating station, the Doctor and Ben encounter a guard on duty. They try the old prisoner and escort routine but are hampered by not knowing the password. However, Ben and the Doctor confuse the guard so much that they not only get through but also learn the password! Upon reaching the power station, they use the password to breeze through. Good thing, as they don't have much time.

Following the Doctor's cue, Ben cuts several power cables in the station. The Doctor adjusts the controls. Almost immediately, the generating equipment's hum changes, clearly indicating an increase in power. The Doctor hopes they've done what they set out to do, and they hurry to Zaroff's lab to find out.

Meanwhile, Jamie and Polly have gotten themselves lost in the tunnels, having made a mistake in following Ara's directions. A low rumbling noise can be heard all around them, issuing from above. They are in the very depths of Atlantis and think that they may be below Zaroff's power source. Hoping this means they are not far from the lab, they press on.

Zaroff has already seen the results of the Doctor's meddling. He fears the increased power could mean a radiation leak and the disruption of his plan.

Polly and Jamie are on a ledge facing a large chasm. Further along the tunnel they can see part of the rock wall glowing brightly. Polly fears radiation but is unable to explain this concept to Jamie. They both can see that the wall is crumbling at the centre of the glowing area. It is the sea wall and soon the water will be breaking through. Unknown to them, it is the Doctor's plan working. Very quickly indeed.

Polly and Jamie abandon their attempt to get to the lab, heading now only for higher ground. They hope they can move faster than the rising water.

Back in the temple, Sean and Jacko can hear the sounds of the sea breaking through. It is happening quickly. Thous knows it is the end of his dream to raise Atlantis from the sea - a dream fed by a madman. He is saddened. The entire group makes plans to head for higher ground.

They are joined by Damon, who was warned by Sean of the impending disaster. He is devastated by the loss of his operating room and his life's work. All washed away. He is shocked to see Thous lying wounded here and goes to his King. Thous will be fine, but there are deeper wounds in him, and all the Atlanteans. Their civilisation is gone and they will have to start again.

Sean suggests the best first step - getting out of here before they drown. Damon joins them, helping Thous to his feet for the journey.

Polly and Jamie reach a dead end, the water encroaching ever closer. Polly despairs of finding a way out but Jamie detects air movement and decides to follow it to its source. Hopefully it will lead them out.

On their way up, Sean and Jacko's party has encountered many Atlanteans and learned of the massive flooding in the lower levels. The Atlantean nightmare of inundation by water has come true. The main shaft is still open for the stragglers, but even the temple is now flooded and despair has gripped the survivors. Lolem was last seen in heading for the temple and is feared dead.

The Atlanteans are united in their loss and have little use for outsiders like Sean and Jacko. The group continues upward in terse silence, Sean wondering what has become of Zaroff.

The Professor is still at his controls in the lab, urging his guards and assistants to stay put. Zaroff refuses to admit defeat and still plans to set off his explosion on cue.

The Doctor and Ben arrive and are promptly seized by the guards. The Doctor begins talking immediately, wondering aloud whether Zaroff's loyal servants realise that he's planning to destroy them all. Some of the technicians are startled at this, as if realising at last what all their secret work has been for. With this information and the news that the sea is breaking through, everyone flees. Only Zaroff, Ben and the Doctor are left. But the mad Professor will not allow himself to be defeated. He activates a control and a metal grille descends, isolating Zaroff and the main controls from the rest of the lab. He has planned for every contingency it seems.

Ben is horrified as Zaroff announces he can still trigger the world-shattering explosion from here. All he must do is wait for the power build-up to be completed and press one button. With a mad fire in his eyes, Zaroff urges the Doctor to stay and watch... and to die with him.

The Doctor has other ideas.

Jamie and Polly track the air source to a very small shaft in the rock wall. It is their only chance and they crawl in just as the water reaches them. They still have a long way to go.

Ben appears to become worried as the sounds of water grow louder in the lab and he asks to be allowed to leave. The Doctor reluctantly agrees and Ben dashes off. Zaroff laughs at this "desertion". It is only the two of them now and it will not be long before the power is at critical.

The Doctor manages to disable the power system in the lab and the lights go out. As expected, Zaroff is forced to raise the grille and come out to turn the power back on. He covers the Doctor with his pistol and starts to tie him up to keep him from further mischief.

However, Ben's defection was only a ruse and he dashes back in, heading for the main control panel. Zaroff shoots at him but his aim is off and Ben is able to reach the control to close the grille. It slides down just as Ben gets to the other side. Zaroff is horrified to realise that he is cut off from his equipment. His plans are foiled and the water is now flooding into the lab yet he clamours at the grille, trying in vain to reach the detonation control. The Doctor and Ben escape.

Some ways up the main shaft, the Doctor finds his conscience burning. He did not expect Zaroff to stay in the lab and he fears he will drown. Despite Ben's objections, the Doctor turns back.

Polly is tiring rapidly on their seemingly endless uphill climb. She refuses to go another step, nearly hysterical with fear and exhaustion. Jamie urges her onward, knowing they must hurry or die right here.

The Doctor and Ben cannot get to the lab now. The rising water has already cut them off. Inside, Zaroff clings to the grill in desperation as the sea surges all around him.

The Doctor and Ben race for the surface, now realising they know nothing of the fates of their friends. Both are worried.

Polly and Jamie finally emerge into daylight and fresh air. They are grateful to have survived. As they look about the rocky shore of the island, they see others emerging. But there is no sign of the Doctor or Ben.

Sean, Jacko, Thous, Ara, and Damon have also made it. They, too, fear that the Doctor has been drowned saving them from Zaroff's evil. Thous plans to raise a monument to the Doctor in the new temple, but Damon is adamant that there be no more temples. Their belief in the ancient superstitions is what allowed Zaroff to control and manipulate them. It must not be allowed to happen again. The temple will remain underwater forever, and the new Atlantis will have no place for Amdo... and no need for fish people.

On the surface, Polly and Jamie are startled by a sound behind them. To their great surprise and relief, it is the Doctor and Ben. Their reunion is joyous.

The Doctor wastes no time heading for the TARDIS.

Sean and Jacko, exploring the beach, come across a very incongruous English police box. They are even more startled to watch it fade away with a grinding engine noise.

The Doctor and his friends are happily ensconced in the ship and ready to put their "fishy' adventure behind them. Even the newcomer, Jamie, is pleased with their travels so far. He feels happy and safe in the TARDIS as well, despite the fact that the Doctor can't control it.

The Doctor takes offence at this remark and announces that he could control it if he wanted to; he just has never wanted to. To prove it, he decides to take them all to Mars.

He operates the steering controls with confidence, but the ship immediately lurches and its normal calm hum goes into overdrive. The occupants are tossed wildly about, unable to hang on as the ship lurches and shudders.