Barbara is first out of the TARDIS, followed by the others. Clearly no one has noticed the radiation counter on the console and its insistent warning. Unbeknownst to them, the forest is full of deadly radiation. Barbara thinks instead that the extensive damage to the plants could have been caused by a fire as the plants are ashy and grey. Ian notes the lack of a breeze and touches a tree branch. It crumbles in his hand, like weak stone. The Doctor is fascinated by all of this, calling the place a petrified forest. It clearly was neither heat nor age which destroyed the former jungle. He intends to find out the cause and moves off to investigate further. Susan follows.

Ian and Barbara take a moment to size up the situation. They have no way of knowing where they are, but it is certainly not home. Ian is beginning to seriously doubt whether the Doctor can get them home at all. Barbara suggests they keep near the ship for safety, but Ian points out that it's no use to them without the Doctor to fly it. They should stay with him - he seems to have a knack of finding trouble. Barbara agrees, trying to keep her fear of this unknown situation in check.

They rejoin the Doctor and Susan a little ways into the jungle. Susan has found a flower on the ground in perfect condition, even retaining a little of its colour. Ian kneels to help her pick the fragile plant whilst the Doctor examines a tree nearby. Barbara, however, has wandered off. Suddenly her frightened scream breaks the silence. Ian hurries to her, accidentally crushing Susan's flower in his haste. She drops the broken and dusty thing after a moment's sadness, then joins her grandfather as he moves toward Barbara.

Barbara has found a small reptilian creature on the ground. It is vicious-looking with a pointed snout, long teeth, and red eyes. Most strange of all is the metallic appearance of its skin. After a moment during which the creature doesn't move at all, Ian bends down to examine it despite Barbara's protests. He waves a hand in front of it and there is no reaction. He soon realises that this creature is like everything else here: dead. The Doctor examines it and notes a startling fact: the creature is made of metal, even when it was alive. Ian dismisses this as impossible, prompting an impatient response from the Doctor. Not all living things must be made of flesh and bone. This creature's skin is a pliable metal, held together by a magnetic field. It makes perfect sense to him. This is clearly not Earth and Earth standards do not apply. He moves off to explore further. Susan joins him, noting that the jungle seems to thin out ahead.

The Doctor has admitted that their previous journey was far too hurried to allow for a planned landing place, leaving open some hope of getting home, but that is precious little for Barbara to count on. She is an unwilling adventurer and despairs of ever getting back home. Ian tries his best to reassure her, telling her not to give up hope and to rely on him to help her through. This seems to help.

Susan rejoins them, saying that the Doctor is going to try and fix their position using the stars. Barbara is concerned at this, thinking it a bit primitive compared to all the equipment in the ship. Susan says the TARDIS has a computer which can compute their location and even fly the ship, but it must be fed with the right sort of information and her grandfather is usually too preoccupied with his researches to gather the data required. She also admits he is somewhat forgetful.

Ian wanders off to explore a bit more as the Doctor joins the girls. Although he cannot answer the question of why, his investigations show that this planet is totally dead. He is interrupted by a shout from Ian which brings them all running. Ian stands on the edge of a precipice which overlooks a large valley. Down below them, they can all see what caught Ian's attention - a massive, sprawling metallic city. It has towers and spires and roads, all gleaming metal. It is fascinating and strangely beautiful. The Doctor examines it through an odd sort of binoculars but detects no movements. Whatever destroyed the jungle killed the city's inhabitants but left the buildings intact.

The Doctor announces his intention to go down and explore the city, which draws a harsh response from Barbara. The Doctor is determined to have is way but relents for now when Ian and Susan point out the gathering darkness. Ian is against the venture himself, not wanting to put them all in danger, but he also doesn't want the Doctor going alone as he is the only one who can operate the TARDIS. In this atmosphere of hostility, the group heads back to the ship.

The trip is slow going as the darkness increases. As they move through the jungle, Susan lags behind, her gaze caught by another of the beautiful petrified flowers. She stops to pick it, unseen by the others as they move on. Suddenly she becomes aware of another presence near her. With fear in her voice, she calls out, trying to locate whatever is there. She sees nothing, but starts at a strange sound. She is on her feet, her eyes wide with fear, trying to pick out anything in the ashy gloom. Suddenly a hand reaches out from the darkness behind her and touches her shoulder. Susan screams and runs blindly in the direction of the TARDIS. She is caught by a worried Ian, who grabs her in his arms and tries to calm the sobbing girl.

Some time later the group is safe in the TARDIS. The Doctor has been speaking to Susan, trying to find out what frightened her. He has tried to explain that there can't be anyone left alive on this planet and that she must have imagined the touch. But he is sure she has not listened to him and appeals to Barbara - somewhat clumsily but with considerable charm - to talk with the girl. He thinks she may listen to someone closer to her own age.

Barbara goes back into the ship's living area where Susan sits drawing a picture of the flower from the jungle. Barbara carefully broaches the subject of what happened outside, hoping to ease the girl's fear. But Susan has moved beyond fear to anger that no one believes her story. She even gives Barbara a quick tap on the shoulder to demonstrate how she couldn't have been mistaken. Barbara says she believes Susan and tries to explain the Doctor's doubt as stemming from his adherence to scientific fact. She urges the girl to try and forget it for now, at least until they learn more.

In the console room, Ian watches as the Doctor examines a bank of machines along one wall. He is making notes and is paying little attention to Ian's attempts to question him. Finally the chatter gets too much and the Doctor rounds on him. Ian tries to calm him down; after all they are fellow travellers for the time being. He simply has lots of questions about all this as he and Barbara are completely out of their element. The Doctor reminds him that they forced their way into the ship and bear much of the blame for their current situation. He ignores Ian's questions until the subject of food comes up. The Doctor wanders off toward the living quarters for some food, Ian following after.

Inside, Susan is fixing up a headache remedy for Barbara. She apologises for her earlier "silliness". All is forgiven as the Doctor turns his attention to a machine sitting in a corner. Barbara drinks her medicine and watches as the Doctor activates some buttons and dials. The Doctor removes a wrapped cube from the machine, opens and eats it. He is nearly finished before he notices that Ian and Barbara are waiting for an explanation.

The Doctor asks them blandly if they'd like something to eat. Dubiously, they both settle on bacon and eggs. After a moment of work between the Doctor and Susan, the machine produces two more cubes. Ian is first to overcome his disbelief and bite into the "food". To his astonishment, the cube tastes just like eggs and (slightly salty) bacon. Barbara eats ravenously. The Doctor explains that flavours are a bit like colours in that they can be blended together. This machine takes the "component parts" of different foods and puts them together to make anything desired.

Barbara's headache is now gone and she is well fed. However, Susan isn't hungry - an unusual occurrence. She would much rather sleep, but before she can turn to go, a knocking sound issues from outside the ship. All 4 freeze and listen as this is followed by a scraping sound and another knock. They all hurry to the scanner as Susan exclaims that she was right. Someone is outside.

However, the scanner reveals nothing. Barbara has had enough and asks the Doctor if they can leave this planet. He protests that he still wants to visit the metal city and mutters darkly about uninvited passengers trying to tell him what to do. But when Ian and Susan join the protests, he appears to relent. Without a further word, he activates a series of switches. Ian, Barbara, and Susan all relax and turn back toward the scanner.

As soon as he is unobserved, the Doctor hurriedly removes a small component from the console and conceals it in his hand. He throws another switch and the engine noises begin to rise as the ship prepares for flight. However, a loud boom interrupts the sequence and the engine noise fades to silence. The Doctor's face is a mask of worry as he examines the controls. A second attempt at take off produces the same non-result. Hunched over the console, the Doctor deflects Ian's questions and sends Susan to the fault locator to trace the problem.

From one of the machines against the wall, Susan reads out the component K7 and the Doctor knows immediately it is the "fluid link". He makes a move as if he is removing a part from the console, but comes up with the same part he removed earlier. It is a small metal cylinder whose top the Doctor says has come loose, spilling out all the liquid inside. But he says it can be repaired easily by refilling it with mercury. However, there is no mercury in the ship as a supply has never been needed before. Ian and Barbara are taken aback at this dangerous inefficiency. Where can they possibly find mercury on this desolate planet? It dawns on them both at once: the city. The Doctor's voice drips with innocence as he pretends to realise this for the first time. Suspicion grows in both Ian and Barbara as they agree to head for the city at first light. They do not see the Doctor's satisfied smile.

The next morning, after a quick check of the scanner, the group is ready to depart. Ian reminds the Doctor that finding mercury is their only goal. Then it's straight back to the ship. The Doctor agrees easily and off they go. Stepping outside, they see a small metal box near the ship. Ian is concerned it may be a bomb and prods it carefully with a petrified stick. When it seems safe, he picks it up and opens it to reveal a series of glass phials all filled with an amber liquid.

Susan is vindicated and Ian apologises for doubting her. The Doctor wishes to run some tests on the liquid and has Susan put the box in the ship for safekeeping. Again they prepare to set out. Susan confirms she has a day's supply of food for all of them, prompting concern from Ian. He feels it is an excessive amount of food for what should be only a couple hours' trip. His suspicion of the Doctor grows further as they all head off.

After an arduous journey, the group arrives in the city, at the main entrance to a building. As they suspected, the entire city is made of metal. There are no stairs, only ramps, and the doorways before them are squat rounded arches. All the doors are closed. The Doctor is nearly exhausted, leaning on Susan for support. He wishes to rest, but refuses to let Ian and Barbara look around on their own. Ian, too, is complaining of fatigue, an unusual occurrence for him. He urges them all to keep to the task at hand, looking for a laboratory or supply room. They should be able to find mercury easily.

Barbara has been examining one of the archways, concentrating on what looks to be an opening mechanism off to one side. She passes her hand across the face of it and suddenly the door before her glides up. A corridor lies beyond. Ian decides their search should commence right away. They will split up and meet back here in 10 minutes. Barbara enters the corridor she has opened while the Doctor and Susan move off to find another doorway. Ian opens a nearby door and goes inside.

Barbara finds the corridor the same as the doorway - squat and rounded. She must duck her head to get through in places. The walls are shiny and nearly featureless. She does not notice the stalk-like camera which is set into one wall. It turns and follows her as she passes.

The Doctor and Susan go a short way along the outside of the building and find another doorway inside. Susan opens it and - still supporting her grandfather - leads the way inside.

Barbara moves slowly down the corridor, stopping occasionally to examine the wall for any unseen doorways. She finds nothing and must keep going. She does not notice as a shutter slides silently down behind her, cutting off any possible retreat. As she goes, more shutters close. Eventually she reaches a T junction. Turning the corner reveals a dead end. Turning to go back, she becomes aware of the shutters. Her way back is now blocked. Barbara pounds on the shutter in frustration, trying in vain to open it. Her fear growing, she turns and runs down the only corridor still open to her.

Back at the rendezvous point, Ian welcomes the arrival of the Doctor and Susan. None of them has had any luck finding mercury. There is also no sign of Barbara. Ian tries to hold back his concern, giving her 2 more minutes. If she's not back, they'll have to go after her.

Barbara runs headlong into another dead end. Her fear grows. There are shutters on either side as well. She pounds on one of them, the sudden noise deafening in the silence of the city. With a force of will she controls her fear and the tears which threaten to spring into her eyes. Composed, she moves to go back the way she came. Suddenly a fourth shutter slides down and she is trapped in a very small cubicle. To her greater horror, the entire cubicle begins to descend.

Outside, Ian grows impatient. They must go in search of Barbara. He opens the door she used and all three disappear into the corridor.

Ian, Susan, and the Doctor move into the corridor down which Barbara disappeared. There is no sign of her or her path, but the Doctor stops them all when he detects a quiet mechanical ticking sound nearby. They all move toward it, Susan still supporting her grandfather. Just down the hall they find a door. The noise is louder here. Ian opens the door and they venture inside.

They find a large room full of scientific instruments of a very sophisticated nature, all of them still active. The Doctor is overjoyed, realising this means there is a very advanced civilisation still in residence here in the city. Ian is concerned, though, about just who or what they might be. But the Doctor does not care, preferring to examine the instruments. However, his joy turns to fear when he realises that the machine emitting the ticking noises is a Geiger counter; it's needle is in an obvious danger zone.

This information provides an answer to the mystery of the petrified jungle: a massive neutron bomb must have been detonated which charred the plants, animals, and soil, yet left all the buildings intact. All three of the travellers realise they've been walking around unprotected in the midst of unimaginable nuclear fallout. That is why they've all been tired and ill. They are in grave danger unless treated with anti-radiation drugs very soon. Susan is not worried, sure the TARDIS can take them all to a place where they can be cured. However, Ian reminds her that the ship cannot move until they find mercury for the fluid link. It is then that the Doctor is forced to confess that he lied - there is nothing wrong with the fluid link.

Susan and Ian are aghast at this deception, the latter lashing out at the Doctor furiously. He takes the fluid link away from the Doctor, trying to fathom the depth of their danger. The Doctor knows that Ian's abuse is warranted, but he'd rather wait until they are safely back in the ship before recriminations begin. Ian tells him sternly that they cannot leave until they've found Barbara, and he holds the fluid link hostage to force the Doctor to stay. It is time, Ian says, that the Doctor faced up to his responsibilities. Susan agrees, urging her grandfather not to waste any more time. He agrees in a huff and the three of them move off to renew their search.

They emerge into another large room with several corridors leading off. Almost immediately, a swarm of hideous metal machine creatures burst from every corridor and surround them. They are squat and rounded with no discernable humanoid features. A single lens on a stalk functions as an eye; they move on hidden wheels and possess two stubby "arms". One of these has a sucker on the end - like the one that menaced Barbara - and the other is clearly a weapon of some sort. The Doctor, Ian, and Susan freeze in horror. In a harsh, halting, mechanical voice, one of the creatures orders the travellers to move forward into a corridor. Ian attempts to make a break for it, but the creature fires its weapon. Ian cries out in pain and collapses to the floor, bathed in a ray of energy.

The creatures tells Ian that that his legs have been paralysed. He will recover, but a second burst of energy will make the condition permanent. Suitably subdued, the Doctor and Susan obey an order to help Ian up. The three of them are now prisoners.

They are taken to a cell and tossed inside. Barbara is already there, looking much the worse for her ordeal but otherwise unharmed. She is happy to see them all again, but concerned over Ian's condition. He is angry with himself for his rashness, but he assures his fellow travellers that his legs are slowly regaining feeling. The Doctor collapses against a wall, the radiation sickness taking its toll.

Barbara tells the story of her capture and how she was transported by lifts for some time before she ended up here. She believes they must be far underground. They all wonder about the nature of these machine creatures and whether they are just robots or if there's something inside the casings. Barbara fears the creatures may have drugged her as she's felt so weak and giddy since her capture, but Ian gives her the bad news - it is radiation sickness. The Doctor sums it up, his voice weak with fatigue: unless they get treatment, they shall all die.

In a nearby control room, a group of the machine creatures observes the prisoners on a viewscreen. They are concerned about these strange creatures, despite the fact that they are firmly imprisoned. Even though the radiation count on the surface of the planet has been significantly reduced, it is still deadly. The prisoners are showing signs of radiation sickness. This is puzzling as the machine creatures believe their prisoners to be "Thals", another of the indigenous races on this planet. If the Thals are still alive as a race, they must have perfected an anti-radiation drug; if these are Thals, then why is the drug suddenly not working.

The Doctor is brought in for interrogation, sinking weakly to the floor. They question him as if he is a Thal, leading to much initial confusion. The creatures believe the Thals have run out of their radiation drug and have come to the city seeking more. The Doctor of course denies this, but he realises that the phials left outside the TARDIS must have been drugs - the anti-radiation drugs he and his friends need to survive. He offers to go - under escort - back to the ship to retrieve the phials. However, the creatures reveal they cannot move off of metal and therefore cannot leave the city. One of the travellers must go while the others remain as hostages. The Doctor seems momentarily reenergised by this ray of hope, but as this offer is agreed to, his fleeting strength ebbs once again.

The Doctor learns that these machine creatures are called Daleks, the remains of once-humanoid creatures now encased in protective metal shells. The Daleks and the Thals fought a neutronic war. The Daleks have survived cocooned in their city and their casings. They have recently learned that some Thals survived as well, but none have been seen. The Daleks believe the Thals to be hideously mutated and the Doctor detects some fear in the Daleks over this. He, too, is afraid. One of his party must now venture out into the wasteland and brave the Thal creatures all alone to retrieve the drugs.

Back in the cell, Ian is trying to walk, supported by Barbara and Susan. For a moment, it looks like enough of the feeling has returned, but Ian shortly topples over. It will still be some time before he can walk. Barbara collapses as well, exhausted and ill. Only Susan seems unaffected by the radiation poisoning.

The Doctor returns and relays the details of the deal he's made with the Daleks. It is unclear which of them can and should make the journey back to the TARDIS. The Doctor also relays details of the neutronic war and the Thal mutations. Ian is convinced that he must go on the journey and the Doctor is too weak to argue. He lapses into mild catatonia. Susan tells Ian she must go with him, a prospect he will not accept. But when Susan explains to him the complex 21-tumbler security feature of the TARDIS lock and assures him he will be unable to get in, he agrees. But all of that is moot when it becomes clear that Ian is still unable to walk.

A Dalek arrives to escort one of them to the surface. Susan is horrified when it appears that she is the only one able to make the journey and that she must go alone. Barbara is dizzy and can barely stand. She pleads with Ian to try and delay the trip, but the Dalek insists it must be now. Ian also knows that he and the others cannot wait much longer for the vital drug; he has no choice but to let Susan go, to save their lives and to appease the Daleks. He gives her all the encouragement he can before the Dalek shoves Susan out of the cell.

In the control room, the Daleks cluster around their instruments, tracking Susan's movements. They appear unconvinced that their prisoners are not Thals and they fully expect Susan to make contact with others. They also have no intention of allowing the prisoners to use the anti-radiation drugs if Susan returns with them. They only want to analyse and duplicate the drug for their own use - their prisoners have no value and will die.

In their cell, Ian and Barbara try to fight the illness which is overtaking them. The Doctor is still unconscious and they are sure they will soon follow. All hopes of escape have been dashed due to their weakness and Ian blames the Doctor once again. But he knows that it is a waste of strength and they must pin their hopes on Susan. She has been gone for an hour and must now be on the edge of the jungle.

Susan has indeed reached the jungle, just as a thunderstorm begins to brew. Lightning flashes illuminate the grotesque petrified trees and there is no beauty in this jungle now. Susan becomes more and more frightened and she begins running carelessly. Each lightning flash casts twisted shadows and she is sure that each one is a misshapen Thal mutation. She runs faster, the thunder echoing in her ears. Suddenly, she trips and falls. Pushing herself up, she gasps in horror at what she sees before her.

Barbara's condition, meanwhile has worsened. Like the Doctor, she is now running a fever and all she wants to do is sleep. Ian lets her rest, his hope waning. He isn't sure that the drugs would be in time even if Susan were to return right now. And he knows she still has a long way to travel.

Desperation seizes Susan. Scrabbling in the ashy sand, she hits upon an idea. She chucks a handful of sand at the apparition before her, hoping she's hit its eyes. She runs away as fast as she can, unaware that there really is nothing there.

The Daleks become aware of the desperate situation of their prisoners. The Doctor is dying and the other two are weakening fast. The Dalek scopes have tracked Susan as far as they can - now she is out of range.

Susan reaches the TARDIS at a dead run, gasping for breath. She wastes no time in going inside, closing the door behind her. She picks up the metal box containing what she hopes is the medicine to save all of their lives. But it suddenly dawns on her that this nightmare is not over - she must still get back to the city. She hesitates, Ian's words of encouragement coming back to her.

Susan emerges from the ship, but stops dead in her tracks when she catches sight of a man standing on some rocks nearby. She sinks to the ground, unable to run, but the man assures her there is no need to be afraid. As the sky lightens, she can see this is so. This man - presumably a Thal - is no hideous mutant. He is tall, lithe, muscular and handsome with short blond hair. Susan calls him "perfect".

The man explains that he was the one who frightened Susan in the jungle the day before. He apologises for being so "clumsy" in trying to make contact. He was also the one who left the drugs for them to find - it was no accident - and he wants to make sure that she and her friends have used them properly. The man is horrified to find out that they have not used the drugs and Susan tries to tell the story of their capture by the Daleks. But she is nervous and her words tumble out. The man calms her and tries to get the details.

The Thals had been unaware that the Daleks had survived the neutronic war. The man, Alydon, cannot understand why the Daleks should hold these strangers prisoners, nor why they should want the Thal anti-radiation drugs. Surely they have their own drugs if they are still alive in the radioactive post-war world. It occurs to him that the Daleks may not be interested in the drugs for any good reason - they may simply wish to keep them from the travellers. This had not occurred to Susan, even though she doesn't entirely trust the Daleks.

Alydon offers Susan a second supply of the vital drugs, which she hides on her person. He also offers her his cloak to keep her warm and offers to escort her safely back to the city. As he prepares to go, he marvels at the thought that the Daleks survived the war. He also wonders what sort of creatures the Daleks must now be...if they think of the Thals as "mutations".

Susan returns quickly to the city. The Daleks return her to the others, then regroup in their central control room. They agree to give the prisoners water and then consider their next move. They are certain that Susan made contact with the Thals, and they appear pleased that this contact may bring the Thals to them.

In the cell, Barbara and Ian are already beginning to recover, thanks to the Thal drug. The Doctor is still unconscious, but his pulse is now steady and his fever has dropped. They will all recover, thanks to Alydon. But perhaps they have the Daleks to thank as well. Susan reveals that the creatures found the second supply of drugs and nearly confiscated it. But they at last gave it back to her, clearly allowing her the opportunity to save herself and the others. Despite this, though, it seems clear that the Thals are the friendlier of the two groups here.

The Doctor awakens for a moment, somewhat delirious still. Susan comforts him and he drifts back to sleep. Susan relays more details about the Thals to Ian and Barbara. They wish her to speak with the Daleks and ask them for assistance. The Thals are on the verge of starvation, the few crops they had managed to grow after the war now threatened by a long overdue rainy season. They had been searching for a new food source, but found nothing. Now that they know the Daleks are still alive, Alydon and his people hope to broker a treaty for food. Without it, the Thals will die.

Unbeknownst to the prisoners, their conversation is being monitored by the Daleks. A camera mounted near the ceiling relays sound and images to the Dalek control room. The Daleks are afraid that the Thals will attack the city out of desperation if no treaty is made. They decide to allow contact with the Thals - to offer them a promise of help. They will try to lull the prisoners into a false sense of security in order to assist with this plan.

The next morning, the Daleks provide food and more water to the fully-recovered prisoners. But they take Susan away with them. The Daleks reveal they are planning to help the Thals, but this does not make the travellers feel better. It makes them realise that they have been overheard!

Meanwhile, Alydon has gotten word to his people about Susan and the Daleks and the hope that they may at last find food. He has waited in the jungle clearing near the TARDIS, and now the other Thals have arrived. There is another young man, Ganatus, and a young woman called Dyoni among them. The Thal group is led by a distinguished older man called Temmosus. Alydon greets them all warmly. Dyoni is intrigued by the strange blue box, but Temmosus is more concerned about the Daleks and this alliance that Alydon has proposed.

Temmosus wonders how the Daleks may have changed over the centuries of isolation since the war. His people have evolved from warriors into farmers. How will the Daleks - former teachers and philosophers - have changed? Will the old hatreds still survive or will they be able to make peace. Alydon is unsure, although he has seen their fantastic city and fancies the Daleks more scientifically-orientated than before. Alydon also expresses absolute trust in Susan and her friends, even though they are clearly strangers to this world. He tells Temmosus and the others that Susan has promised to relay a message to the Daleks. The Daleks seem very suspicious of others, but he still hopes to get through to them. They must await word from Susan.

During this conversation, Dyoni's mood has turned dark. She appears to be jealous of Alydon's faith and admiration for Susan. Alydon is mystified, but Temmosus explains: Dyoni hopes to be married to Alydon once this food situation is resolved, even though he seems indifferent to it. But Temmosus agrees that such talk of the future must wait for now, until the future of their whole people is secured. They await a written message from Susan, signed with her name. If it is unsigned, or no message comes at all, they should assume that the Daleks are hostile toward them.

In the Dalek control room, Susan is transcribing a message from the Daleks, offering fresh food and water to the Thals. In exchange, they say they want the Thals' help in recultivating the land around the city, but Susan tells them she cannot accept this condition, only pass it on to the Thals. Satisfied with the Daleks' sincerity, Susan finishes the message and signs her name as she promised Alydon. The Daleks realise that her signature is a signal to the Thals and are pleased. Susan is sent back to her cell and the Daleks plan to deliver the message themselves. It is becoming more and more clear that their motives are not honourable.

Back in the cell, Susan has related all that she has learned. Their suspicions of Dalek treachery confirmed, the captives are now ready to go on the offensive. The Doctor and Ian stage an argument where the Doctor supports the Daleks and Ian confronts him. It escalates and Barbara and Susan join in. Susan leaps up on Ian's shoulders as the struggle continues, where she can now grab and detach the camera lens from the top of the wall. They have succeeded in destroying the Dalek surveillance device and the group is jubilant.

The Daleks do not seem fooled by this ploy, but neither are they threatened. They believe the prisoners cannot escape and so turn their attention to the Thals first.

Now able to talk freely, the travellers try to determine some means of escape. Brute force won't work against the metal creatures, nor will simply trying to outrun them. The group agrees they must try to put one out of action before they can escape and move freely through the city. And for that they must think. With the scant information they have gleaned about the Daleks, the Doctor deduces that the machines must be powered by static electricity - that is why they can only move on metal floors and emit an acrid smell while moving. This gives Ian an idea. He examines the cloak Alydon gave Susan. It is a synthetic material, not quite plastic, not quite nylon. But it appears to be a perfect insulator, ideal for stopping a Dalek dead.

More Thals have encamped at the clearing, bringing all of the nomads' belongings. In a scouting expedition, the Thals have found the metal creature Barbara stumbled upon earlier. Dyoni calls it a magnedon and seems pleased to see it. She runs off to tell Ganatus' brother, Antodus, about it. Meanwhile, Temmosus has been waiting for Susan's message. He seems calm and composed in the face of the unbroken waiting. He tells Alydon that he believes the Daleks hold the key to the Thals' future, no matter what it is. Despite the risks, he believes their people will survive this adversity as they have done for so long already.

Suddenly, a Thal brings Susan's message to Ganatus. It had been left by the city gates, but there was no sign of Susan or anyone else. Temmosus reads it and is pleased by what it says: the Daleks hold no malice toward the Thals and they look forward to building a new, peaceful, prosperous world. As a gesture of good faith, the Thals are to pick up a quantity of food tomorrow in the entrance hall of the city's main building. All of the Thals are excited by this prospect of hope, and Temmosus belief in a future for his people is even stronger now.

A Dalek comes to deliver food to the prisoners. As it does so, all four of the travellers watch intently, looking for any clues how to disable the creature. After the Dalek leaves, they report their findings. Ian is sure he can jam the cell door open with a piece of the broken camera. Susan and Barbara watched the creature's eyestalk, however, and are less optimistic. The lens seems able to cover a wide area and it will be difficult to sneak up on the creature. Everyone suggests trying to throw a coat over the lens, but Barbara comes up with a better idea. She grabs Susan's shoes and starts to scrape the dirt off of them into a bowl of water. She is making mud.

Some time later, the group is ready to attempt their escape. They are certain a Dalek guard will be in to bring them more food shortly. Susan spreads Alydon's cloak in the middle of the floor, Barbara readies her mud ball, and Ian stand by to jam the door. When the Dalek at last arrives, they spring into action. Ian places the metal piece under the door's pivot point and retreats to the back of the cell before he is seen. Susan takes the offered tray and backs away. The door starts to close, but rebounds off the metal in its path. When the Dalek advances to try and clear the blockage, the four prisoners spring into action. Barbara jams her mud ball on to the creature's eyestalk, blocking its vision. Ian and the Doctor struggle to manoeuvre the Dalek onto the cloak, the creature fighting them all the way. Eventually they succeed. As predicted, the Dalek's arms and eyestalk go limp and the screeching voice is silenced. They have succeeded in immobilising it.

After congratulating themselves, they move to the next part of their plan. Ian finds a catch and opens the top of the casing, intending to remove the living creature inside. However, the sight that greets him is hideous and his quickly closes the lid before Susan and Barbara notice. He sends the girls out into the hallway, ostensibly to keep watch. But he really wants to spare them the gruesome sight. Together, he and the Doctor remove the football-sized bundle and deposit it - wrapped in Alydon's cloak - to a corner of the cell.

Ian then climbs down into the casing, planning to pass himself off as a Dalek. Barbara and Susan return to help close the lid. Ian is cramped into the tiny space, but seems OK. The Doctor instructs him to try and sound more like a Dalek - more mechanical and monotone. After Susan wipes the mud off the eyestalk, he can see, but he is unable to make the thing move. They don't have time for him to learn so the Doctor will have to push. Barbara and Susan take their places in front and the group sets out - prisoners and escort. Susan leads the way toward the lift and, hopefully, out.

As the group moves down the corridor, Ian figures out how to make the Dalek casing move. The Doctor joins Susan and Barbara in front as "prisoners". They turn a corner and at the end is a Dalek on guard in front of the reception area for the lift - the lift they need to escape. They press on.

Ian informs the Dalek - in his best mechanical monotone - that the prisoners are wanted for questioning. But when the Dalek hesitates, unsure of his instructions, Susan comes to the rescue. She pretends to run away, allowing herself to be caught by the Dalek guard. Susan is unharmed, but pinned to the wall. Ian takes over holding her as the Dalek opens the door to the lift area. They enter the reception area and the door closes behind them without further incidents.

The Doctor pulls on some wiring and jams the door mechanism. Ian is in a hurry to get out of the casing as he is suffocating. Barbara and the Doctor try to release the clasp but cannot. It is stuck.

Following procedure, the Dalek guard reports to his superiors the successful transfer of the prisoners. He is of course told that no such orders were given and he tries immediately to open the door with no luck. He triggers an alarm and two more Daleks instantly join him.

Hearing the alarm, the Doctor knows their ruse has been discovered. He redoubles his efforts and frees the catch on the Dalek casing. However, the lid is also stuck and will not open, despite his and Barbara's efforts. Even Ian cannot open it from the inside. There is a banging from the other side of the door and Susan goes to examine it. She reports that the door is getting hotter - the Daleks are trying to burn through it. Time is of the essence.

The group tries to move Ian into the lift, but the metal floor has been magnetised and he is immobilised. The casing will not move and Ian cannot get out of the casing. In desperation, he urges the Doctor to get the girls away in the lift. Susan and Barbara resist, but eventually agree. The Doctor promises to send the lift back down for Ian as soon as they reach the top.

The Dalek cutting tools burn a line along the inside of the door, working rapidly. Ian continues to try and push his way out of the casing.

The lift begins its ascent toward the surface, but Barbara and Susan are still upset at the decision to leave Ian. Knowing the lift is Ian's only chance of escape, Susan tries to push the buttons and send them back down for them, but the Doctor stops her. He knows that Ian made the only decision he could.

The efficient Daleks are nearly through the door as the lift reaches the top. The Doctor sends the lift back down to Ian as promised, but Barbara is angry at leaving him in the first place. She is certain it will be too late for him.

But it is not too late. The Daleks complete their cutting and burst through the smoking doorway. They open fire immediately, destroying the casing. However, upon examination, they see that it is empty. Ian managed to open the lid and get out just before they came through. The delay was enough for Ian; the Daleks see the lift almost back at the top. Ian is aboard. They engage the emergency circuit to bring it back down just before it reaches the top.

On the upper floor, Ian's fellow travellers see his head appear over the floor as the lift rises, but it stops suddenly before he can get out. He throws himself out as the lift starts to descend again and the others help drag him out to safety.

The travellers find themselves in another featureless anteroom with only one door for an exit. There is also a window, which they examine first. They are on the very top of the main building, very high up. They can see the route to the jungle and they try to visualise the maze-like streets they need to traverse to get there. But Barbara notices something else - movement along one street nearby. It is not a Dalek, but a humanoid. They all realise it is the Thals. They are coming for the promised food supplies - and walking straight into an ambush.

At the base of the lift, one Dalek is entering. His orders are clear - he is to exterminate the fugitives. Ex-ter-mi-nate! The lift rises rapidly.

The four travellers pound on the window and try to shout a warning to the Thals below, but the room is clearly soundproof. They cannot make themselves heard. They must escape from here and get down to the Thals to warn them. However, the only door is magnetised and won't budge. Added to that, they soon notice the lift ascending toward them. The Doctor sets to work trying to open the door while Ian, Barbara, and Susan try to stop the lift.

The lift's controls are inoperable, but Ian gets another idea when he spots a large abstract metal statue in one corner of the room. With the girls' help, he pushes the heavy statue to the edge of the open lift shaft and pushes it over, just as the Doctor succeeds in opening the door. The statue crashes down onto the top of the lift, shoving it to the ground with deadly force. The Dalek is crushed and the lift destroyed. The travellers hurry through the open door.

Down in the city streets, the Thals move toward the main building. Alydon is very cautious, suspicious of the Dalek offer of help. He is certain the Daleks were none too pleased to find that the Thals survived the war and he finds their assistance unlikely at best. But Temmosus is calm and assured. He walks openly through the streets and denounces Alydon's fears. The fact is that they need food and the Daleks have offered it. They must take this opportunity and have faith that it is the true start of friendship between their peoples.

In the central reception area, piles and boxes of food are waiting for the Thals as promised. But there are also a number of Daleks waiting in ambush in the doorway recesses. They hide in shadow as the Thals approach.

The travellers have reached street level. The Doctor is ready to abandon the Thals and make for the safety of the TARDIS, but Susan and Barbara remind him that the Thals saved their lives with their anti-radiation drugs. They cannot let the Thals walk into a trap. Ian agrees on both counts, deciding to send the others back to the ship while he alone warns the Thals. They all agree that he stands a better chance of success on his own and the others hurry off. Ian watches until they are safely out of sight and then hurries to try and find the Thals.

Temmosus and the others reach the reception area. Temmosus emerges into the centre on his own and addresses the Daleks he is sure are listening to him somewhere. He makes an impassioned please for an end to enmity between them and a renewed hope for their planet to live again. Ian arrives during the speech and watches as Temmosus receives no response. The Thal leader directs his people to begin carting off the supplies laid out for them. It is then that the Daleks move into view, their guns at the ready.

Ian sees this and shouts a warning, but it is too late for Temmosus. He is hit by a blast and killed instantly. The Daleks begin firing randomly, scattering the Thals and killing many. Ian, too, is pursued, but he manages to escape and hide in an alcove. Once the Daleks have moved on, he is able to emerge. He runs into Alydon. After a brief introduction, the two join forces to get themselves and the surviving Thals out of the Dalek city. Alydon is grief-stricken over Temmosus' death and what the future may hold.

Some time later, most of the Thal survivors have regrouped at their camp in the jungle clearing next to the TARDIS. The Doctor, Susan, and Barbara are there as well, having made contact with the Thals at their camp. Things are quiet and calm for the moment. Dyoni has taken the time to show the Doctor some of their history, recorded in books and on metallic tiles. The records go back over half a million years of the history of this planet, Skaro. The Doctor finds it a fascinating historical record and hopes to use their extensive star charts to locate their place in the universe. It may help him program the TARDIS.

Alydon reports a sentry hearing movement in the forest. He fears it may be the Daleks, even though they told the travellers they could only move on metal and couldn't come out of the city. But it turns out to be Antodus and his brother Ganatus. They are the last survivors of the Dalek ambush. They went back thinking that Temmosus might still be alive. But they found that he was dead and brought his body back with them. Antodus is wounded and Barbara and Dyoni tend to his burns.

Alydon is the unanimous choice to replace Temmosus as leader and he must decide their next course of action. He wonders why the Daleks hate the Thals so much, wondering if there's some way to bridge this hatred. Ian suggests xenophobia - dislike for the unlike - a hatred for which there is no cure. It seems to fit, but this would mean the Daleks would be after the Thals forever. It would leave the Thals with attack or perpetual defense as their only options. This notion is repugnant to Alydon and the other Thals. They are avowed pacifists since the war. They would rather run away and find their fate elsewhere.

Ian is confused by this, thinking they are condemning their race to certain extinction by not challenging the Daleks, but Alydon refuses to discuss the matter further. It is clear the Thals are not cowards, so Barbara too cannot figure out why they won't fight, especially in the face of clear Dalek aggression. But their conversation is derailed by the Doctor. He has discovered in the Thal records that both the Thals and the original Daleks - called Dals then - were humanoid. Before the war they were the same. The neutronic radiation caused both people to mutate - the Thals came full circle as perfect humanoids, but the Dals stopped at the creatures in their machines now known as Daleks. The Doctor is fascinated by it all, and so is Ian when the pictures clearly show the Thals as warriors.

But it is all moot now. The Thals are on their own and the travellers are ready to be off. The body of Temmosus is brought past and the Thals are silent in reverence. Ian wishes again to try and help them regain the will to fight, but he knows it's pointless.

In the Dalek control room, the creatures' plans continue uninterrupted. They have duplicated the Thal anti-radiation drug and are preparing to test it on several Dalek individuals. Additionally, they have managed to extend the power of their rangerscopes to reach the jungle. They have several pictures of the Doctor, Susan, Barbara, Ian, and the Thals. It is clear to the Daleks that these two groups have joined forces. In their paranoia, the Daleks are sure that their enemies will soon attack.

Back in the clearing, Ian has tried and failed to convince Alydon to help them recover the fluid link from the city. Barbara presses him to try again, but Ian is reluctant to do so. He doesn't think it right to ask these people to face death for what is not their problem. The Doctor has been unable to duplicate another fluid link, and even if he could, there's still no mercury. His little trick has rebounded badly on them all. Ian has gotten over his anger and wants only to concentrate on getting out of here.

The Doctor knows they cannot succeed against the Daleks alone and would dearly love to have the support of the Thals, a large body of brave people. Ian agrees they would even the odds some, but he sticks to his earlier conviction - he will not ask the Thals to sacrifice their lives for the fluid link. The Doctor thinks this a poor time indeed to stand on morals and Barbara supports him. All of them will surely die here if the Thals don't help. The Daleks' hatred is such that they will find some way out of their city and come after them all.

Ian sees this point of view, but still cannot ask the ultimate sacrifice of the Thals for something so insignificant as the fluid link. If the Thals fight, it must be for their own freedom and their own survival. This is the only way he will agree and decides on a course of action to see if this is possible. He asks the others not to interfere as he puts his plan into action.

Ian gathers the Thals around him and tries to paint a picture of the Daleks coming out of their city to steal the Thals' treasures and to kill them. Alydon refuses to be drawn on this. He can look around and see the devastating results of war. Their planet was destroyed in one day and there will be no more war on Skaro. But Ian thinks this pacifism is only viable now when they are not in any danger. He callously threatens to take their historical treasures to trade with the Daleks for the fluid link, but Alydon says he would not stop him. Ian then escalates his argument, threatening to take Dyoni to the city and exchange her for their freedom. He goes so far as to grab her arm and pull her away. This at last is provocation enough. Alydon grabs Ian and strikes him, knocking him to the ground. It appears that the lives of his people are enough to fight for after all.

In the Dalek city, an emergency is in progress. One by one, all of the Daleks who have been treated with the Thal anti-radiation drug are going out of control and dying. It is clear that the creatures have become acclimated to radiation and can now actually thrive on it. Distribution of the anti-radiation drug is stopped immediately. But a new problem becomes apparent. The radiation level of the planet is falling steadily now; if the Daleks are to survive, they will need more radiation, not less. It may actually be necessary for them to explode another neutron bomb.

Night has fallen in the jungle and most of the Thals are asleep. The mantle of leadership weighs heavily on Alydon and he is wide awake. Dyoni is with him. Neither of them regret Alydon's action in striking Ian. They do value their lives, but Alydon fears abandoning their long-held principles, even though the cause is just. He still must decide what to do.

On the other side of the clearing, Barbara and Ganatus are also awake and talking. Both of them wonder what Alydon's decision will be and where that decision will lead them. Barbara notices a glow on the horizon. Ganatus tells her it is a lake filled with dangerous chemicals that cause it to glow. It is full of mutated animals. Three Thals were killed there when it was first discovered. It is the perfect defense for the back of the Dalek city.

In the city, a final experiment is underway. A group of Daleks ill from the anti-radiation drug but still alive are to be subjected to massive doses of radiation in an attempt to "cure" them. If it works, they will have their answer - radiation is now vital to them. If that is the case, then adapting to the outside environment will not be necessary. They can change the environment to suit their needs.

The next day, the travellers and the Thals assemble to hear Alydon's decision. He tells his people that they should help the travellers recover their lost equipment. It is either that or go on a vain search for food, waiting for the day when the Daleks come out of their city to kill them all. By running away, they face death by starvation or ambush. If they fight, they can secure food in abundance in the city and help their friends escape Skaro. His people agree with him and they are united in their resolve to fight the Daleks.

Ganatus produces a map of the area and presents a risky plan of attack. He realised last night that the area of the lakes will be undefended by Daleks because the mutations are thought to be a perfect barrier. The Doctor likes this route, despite the danger posed by the swamp. From there they can cross through the mountains and into the city undetected. He proposes sending one party that way and using a second party to distract the Daleks at the city gates so that the others have an even better chance to succeed. Alydon and Ian agree after some thought and the plan is approved.

In the city, the Daleks monitor a small party led by Ian and Barbara as they approach the city. There is some concern over this, but something more important takes their focus. The results of the radiation treatments are in. Most of the Daleks have recovered from the effects of the anti-radiation drugs. The Daleks must have radiation to survive and begin an immediate inventory of their available nuclear material.

It takes the best part of the day for Ganatus' group to cross the swamp. Night is falling when they arrive at the lake. Antodus looks over the glowing water and shudders in horror, remembering the three men killed here before. He and Ganatus were the only survivors, but the fear seems to have affected the young Antodus more than his brother. Ganatus assures Antodus that they can get through, now that they know what to be careful of. He counsels his brother to keep his fears to himself for the good of the expedition.

Ian, Barbara, and the others arrive and survey the situation. The going will be rougher from now on, with many tricky changes in terrain. They agree to rest for the night, then circling the lake tomorrow before heading into the mountains. They have 2 ½ days to get to the city, per their arrangement with the Doctor. Barbara is tired but still game for the journey, though the eerie lake gives her pause. They still have quite some travelling to do yet.

The group moves forward to the bank of the lake, where they hope to make camp. Suddenly something rises up from the water and Ian must beat it back with a stick. Despite this incident, this seems the best, driest place to make camp. The group spreads out to make a sleeping area with their cloaks. Ganatus goes to start a fire while Barbara starts to prepare food for the group.

Ian goes to another part of the lakeshore a little ways off to splash some water on his face. He is horrified when a loud angry roar issues from the water and a hideous multi-tentacled creature rises up before him. Two luminous eyes pierce the darkness. He breaks and runs back to camp.

Ganatus takes charge of the group as Ian recuperates from his experience. A young man named Kristas is put on guard near the water's edge and the camp is moved up the bank to a safer distance. Ian tries to join in on the watch rotation, but Ganatus thinks it better if he and Barbara rested. They are unused to this kind of nomadic life. They will need their rest.

At dawn, Ganatus wakes Ian. He has slept through the night and no one woke him to take watch. He is a little put out by this slight, but seems grateful for the rest. A young man called Elyon summons Ganatus to the lakeside and Ian hurries to join them. Barbara wakes up as well, rested but longing for a nice comfortable bed.

Elyon shows the others what he has seen. A series of massive pipes rise out of the lake on the far side, climbing up the side of the mountain and disappearing inside. This is the Daleks' water source, and the pipes likely go directly through the mountain to the city. This should make their trip much simpler, although they still must get around the lake. Ian rejects the idea of trying to cross the lake on a raft, the memory of last night's encounter fresh in his mind. It will take most of the day to go around, but Ganatus thinks this the wisest course. He and Ian return to camp while Elyon sets about filling the water bags for the day's journey.

Barbara is handing round cups of hot liquid when Ian and Ganatus return. Ian tells her of the pipes and they exchange hopes that their journey has been made easier. They await only Elyon's return before they break camp.

But before Elyon can even begin filling the bags, the water before him begins to bubble and hiss. A whirlpool begins to form in the water and he is transfixed with fear.

Reaching the lakeside, Ian, Ganatus, Barbara and Kristas see the whirlpool subside. They find the water bags abandoned but no sign of Elyon. Antodus arrives as well and is stunned by yet another loss. The deaths of his people weigh heavily on the young man. Ganatus tries to reassure him and tries to redirect him toward the perilous journey still ahead.

In the jungle, the Doctor, Susan, and Alydon prepare their own upcoming attack plan. Observing the city from a cliff top, they are putting together a map, looking for access points and critical systems to put out of action. The Doctor is particularly concerned to find and knock out the Daleks' radio and television equipment. It gives them complete coverage of the city and makes a surprise assault impossible. If they can knock out these systems, the less-mobile Daleks will be less of a threat. They must hope they can keep the element of surprise, but all the while they worry what the Daleks themselves may be planning.

In the Dalek city, the inventory of nuclear material has been completed. There is not enough material to construct a bomb to saturate the requisite 500 square miles. That would take 23 days to complete. But the radiation level of the planet is falling so fast that they do not have that kind of time. They must find another way of spreading the radiation that has become vital to them.

The expedition led by Ganatus, Ian, and Barbara has found their journey surprisingly easy thus far. They have circled round the Lake of Mutations and climbed the cliffs following the water pipes. Now they are inside the mountain itself. However, things are looking bleak again as they cannot seem to find a cave which goes all the way through. They have been traversing dead end after dead end for some time.

The group has split up, each group chasing down a possible tunnel. Barbara and Ganatus are exploring a passage together. They appear to have found yet another dead end, but Barbara hears water trickling from somewhere nearby. She spots a very narrow fissure just barely wide enough for them to crawl through. Ganatus decides to explore on his own, tying a rope to his belt and giving the other end to Barbara. She urges him to be cautious, echoing Ian's words, but Ganatus challenges her to think for herself. The comment touches a nerve with Barbara.

At the end of the passage, Ganatus finds a drop of about 30 feet. He warns Barbara to tie off the rope so he can lower himself down and explore. However, Barbara's choice of boulder is a poor one. Ganatus only gets part way down when the rope begins to slip. Barbara grabs the rope and holds with all her might, but Ganatus is too heavy for her. She slips and the rope flies from her grip. Ganatus falls to the ledge below, landing roughly.

Barbara calls desperately after him, bringing Ian and Antodus running. But Ganatus is only stunned by the fall. He recovers quickly, assuring them all he is fine. Barbara is mortified at her failure, barely cheered that Ganatus is all right. Ian prepares to bring down another rope to haul him up, but Ganatus instructs him to bring the whole party down instead. He has found a gallery with many tunnels leading off. They may have accidentally found just what they've been searching for.

Meanwhile, the Doctor has not been idle. He has put part of his plan into action. In the Dalek control room, the rangerscopes have detected great activity at the Thal camp, but they cannot receive pictures due to an assault on their receivers. Fearing an immanent attack, they redirect their instruments on the city's entrances instead of the jungle.

The Doctor is leading the Thals in using mirrors against the Daleks. They are reflecting sunlight directly into the receivers, hoping to blind them. The Doctor is sure it has worked, calling a halt to the bombardment for Susan and Alydon. They must hurry for the city while the others continue to distract the Daleks. He wishes to attack one of their central antennae. Alydon carries the makeshift map as the group moves out. The Doctor is eager to show the Daleks a thing or two.

Things are looking up for Ian's party. They have found a tunnel that leads in more or less a straight line, it is broad enough to walk through, and fresh air is getting in. It looks promising indeed. But one member of the party - young Antodus - is still filled with fear. He is certain that they will all die here in the mountain and he wishes to go back now while he still can. All of the death he has seen has made him fearful. Ganatus tries to calm him down, but Antodus only gets more insistent that he and his brother turn back, leaving the others to die. Antodus tries to run, but Ganatus grabs him. There is a struggle in which Ganatus strikes his brother. Both are stunned into silence for a moment.

Suddenly there is a loud crack and part of the roof gives way. Ganatus pulls his brother to safety just before they are both struck. Ian returns, glad to find them both safe. Ganatus tells Ian that it was Antodus who saved them both, cutting his head in the process. Antodus says nothing, but is stung by his brother's charade. Ian can sense that something is wrong between them, but neither betrays the other. Ganatus points out to Ian - and to Antodus - that they cannot go back now as the tunnel is completely blocked by the rock fall.

In their control room, the Daleks have detected intruders at the city walls. They track the intruders not using their rangerscopes but by vibration sensors instead. They hope to maintain surprise this way.

The Doctor, Susan, and Alydon have come alone to the city wall, specifically to the base of the antenna the Doctor noted earlier. At its base is a couple of glass-fronted control boxes. One wire leads out of them and up the side of the antenna. The layout of the box proves to the Doctor that the entire Dalek city is powered by static electricity. To put this antenna out of action, he decides on the direct approach - smashing the glass control rods inside the first box.

However, the Doctor is concerned that this attack - as well as the continuing assault of the reflected sunlight - might provoke a response from the Daleks and he sends Alydon off to his people. They should move their positions from time to time to be safe. He assures Alydon that he and Susan will be fine. Reluctantly, Alydon returns to the jungle.

The Doctor and Susan turn their attention back to the control box, hoping to do even more permanent damage. Using Susan's TARDIS key on the end of his walking stick, the Doctor manages to drain away the residual static electricity from the main box. The same tactic on the smaller box produces a bright electrical flash. The Doctor is pleased with the damage he has done, but Susan worries that they've stayed in one place too long. Her fears are proved right when a group of Daleks suddenly surrounds them. They are prisoners once again.

The tunnel that Ian, Barbara, and the Thals traverse has opened out into a ledge on the side of a cliff. It is still wide enough to walk, but the going has been harder. Ian, in the lead, suddenly stops short. He has nearly walked over the edge of a deep chasm which opens up directly before them. The ledge here gives way to nothingness far below. The ledge continues several feet over. After checking the depth of the chasm by dropping a pebble, Ian and Ganatus realise the only way they can go is across the chasm. They must jump to the other side.

Wasting no time, Ian ties himself off with a rope in order to make the jump. Ganatus and the others hold the other end of the rope. Ian takes a good long run and managed to reach the ledge on the other side. It seems firm enough, but only large enough for two people at a time. Ganatus is the next to make the leap, landing safely with Ian's help. They decide to explore the ledge area a bit further before bringing the others over. The ledge rounds a corner, narrowing precipitously, and Ganatus must press himself flat against the rock face to get around. He reports that the ledge widens nicely on the other side and continues in the same direction. Ian tosses the rope across the chasm for the next person.

The Doctor and Susan are taken to the Dalek control room where they are accused of destroying the Dalek videoscope and a lift. The Doctor reminds them of the deaths of Temmosus and the other Thals. He asks them to forget this enmity and to help the Thals before they starve to death. But total extermination of the Thals is what the Daleks now want. Tomorrow they will release radiation from their nuclear reactors into the atmosphere. When that is done, the Thals will be dead, the Daleks will have the environment they need to live, and they will be the masters of Skaro.

Barbara makes the leap across the chasm successfully. However, she nearly topples over the edge when she tries to round the corner facing the wrong direction. Ian helps her and soon she is safely around. This leaves Antodus and Kristas on the far side. Antodus lets Kristas go before him - as he has done for everyone else - his face a mask of fear and trepidation. Kristas leaps the chasm easily and goes off round the corner. Only Antodus is left.

The young man stares blankly over the edge of the chasm, paralysed with fear. Ian sees this clearly and tries to help with encouraging words. He tosses the rope to Antodus, but the young man makes no move to catch it. He doesn't even acknowledge the rope when it hits him. Worried, Ian orders Antodus to step back from the edge. In a daze, reacting only to the commands, Antodus does so. He obeys again when Ian instructs him to catch the rope and tie it round himself. All the while he is lost in a swirl of fear and doubt. He is certain he can't possibly make the leap.

Still in a daze, Antodus does as he is instructed - backing up and making a run at the chasm. But he is not paying attention and does not jump far enough. He lands on the very edge of the rock ledge and before Ian can get to him, Antodus falls backward into the chasm. Ian drops to the ground, trying to brace himself for the shock that is coming, but when Antodus reaches the end of his slack and his full weight jerks against the rope, Ian loses control of his end.

Ganatus arrives and grabs hold of Ian. This halts his slide for the moment, but he cannot get enough of a toehold to pull both Ian and Antodus back. Ian shouts to Antodus to get a grip on the rocks to take some weight off the rope, but the rock is too smooth. The fear is still in the young man's eyes, but it is slowly replaced by something else - calm resolve. Antodus pulls out a knife and begins sawing away at the rope, his life line.

Ganatus calls back for Kristas to help and Ian joins in the call as he continues to struggle. But there is no time. Suddenly the weight is released from the rope and Ian and Ganatus tumble backward. Antodus is gone. Ian hauls the rope up and shows Ganatus the frayed end. Ganatus can say nothing, an expression of grief on his face. His brother bravely sacrificed his life to save the other two, but in the end his premonition came true. He dies in the caves. What now of the rest of them?

In the Dalek control room, the Doctor and Susan are still prisoners, now clamped to the wall with metal straps. They try to reason with the Daleks, asking them to share the planet with the Thals, to try and live together and work together to solve each group's problems. But the Daleks are set on their plan. To live, they need radiation, which would kill the Thals. Without it, the Daleks will die. Only one race can live and it shall be the Daleks.

Despair haunts the party in the caves. To make things worse, Kristas reports that their way is blocked by an impenetrable rock fall. Ganatus is ready to give up and go back. The deaths of Elyon and Antodus weigh heavily on him. Ian and Barbara try their best to get through to him they must go on so that those men's' deaths are not in vain. But Ganatus believes they will all die here. Suddenly, the light from the Thal fire box dies. Their torch is also getting low on power so they switch it off to conserve it. However, as soon as the artificial lights are extinguished, it becomes clear that there is natural light getting in from somewhere.

Ian springs to his feet and scrabbles along the top of one wall. He finds a hole which he enlarges. Through it he can see the terminus of the pipes from the lake and some large mechanical equipment. They must have been travelling beneath the pipes all along. They've made it through!

Back in the jungle, Alydon, Dyoni, and the other Thals have been waiting for any sign of the Doctor. The Daleks' main antenna has not moved in some time, indicating that it is out of action, but the Doctor and Susan have not returned. Alydon believes they must have been captured. Feeling confident that the surveillance equipment is inoperative, Alydon decides it's time to attack. He rallies his people and they are ready to fight for their survival.

Unbeknownst to the Thals, time is very short indeed. The Daleks are in the final stages of their plan to release nuclear reactor waste into the atmosphere. Desperate to stop or even delay them, the Doctor announces that he possesses a time machine. At first the Daleks do not believe him, but when he reminds them of the fluid link they confiscated - and they examine it more closely - they see he is telling the truth. But when the Doctor tells them where it is located, they are no longer interested in his assistance. They will carry out their nuclear dump, kill everyone, and then go to the jungle and learn how to fly the ship themselves.

The Doctor despairs that his gamble hasn't worked at all, but suddenly an alarm sounds. Vibration sensors have detected Thal intruders. The Doctor's delay was just long enough. The Thals are coming, but will they be able to stop the Daleks?

Ian, Barbara, Ganatus, and Kristas have made it into the city and are searching for the control room. They are nearly caught by a Dalek, but an intruder alert sends it rolling off to another part of the city. Alydon and the others must be here as well.

The Dalek videoscopes soon detect Ian and his party on Level 8, even though he disables the camera as soon as he sees it. Susan and the Doctor see Ian on the screen before it goes blank and are heartened. They shout again to try and stop the Daleks, but the final phase begins. There is an air of frenzy in the control room as the countdown commences from 100.

Ian's group runs into Alydon and his group on Level 9. There is a brief reunion and update. The Thals are spread all over the city, hoping to distract the Daleks. Without the Doctor to guide them, however, the Thals are unsure of their objective. Barbara wants to find the Doctor and Susan, but Ian insists the control room must be their first target. Alydon learns of Antodus' brave sacrifice.

A command issues throughout the city, recalling all Daleks to the control room on Level 10. That's only 1 level away. However, security shutters begin to close all around them, sealing them off from the rest of the city. They are too late to stop two of the shutters, but Kristas stops and holds a third with great difficulty. Barbara is the first one through and she sees another barrier beginning to close ahead of her. She throws herself at it, trying desperately to hold it.

The Daleks are aware of this activity. As the countdown reaches 48, the Daleks increase power to try and force the security barrier down.

The door has nearly pinned Barbara. She is on her back under the door, pushing with all her might. First Ian then Ganatus reach her and try to help. They hold it against the increased pressure but cannot raise it. Barbara is pinned, trying to wriggle out to no avail. Shortly Alydon and Kristas join in. Kristas is the deciding factor and the barrier raises just enough for Barbara to get through. Alydon is next, but none of them are sure they can hold it for long.

In the control room, things are getting more hectic. The countdown continues from 46, but the Thals are starting to arrive. The first one enters, but he is cut down by Dalek fire. The countdown continues.

Ian alone remains on his side of the door, still holding on. Ganatus and Kristas hold from the other. The strain is enormous but they must hold on for Ian's sake. Hurriedly, Ian slides through the gap. Once the resistance is gone, the barrier slams shut.

From here, things happen rapidly. Ian and the others reach the control room area as the countdown reaches 40. They aren't sure what is being counted, but they know it isn't good. Avoiding one Dalek, the group edges toward the control room. They catch sight of Susan and the Doctor clamped to the wall. They are positioned out of direct sight of the Daleks in the room, so Ian and Alydon go to release them.

Barbara goes on the offensive, striking a Dalek with a rock. It does no damage of course, but the Dalek follows after her, firing. Barbara avoids the weapon and with the help of two Thals, she uses a rope to trap the creature.

The Doctor and Susan are free but are hampered in their movements by the Doctor. Ian distracts a Dalek as it turns to fire and saves them. They manage to get away from the fighting. The countdown has reached 7.

More and more Thals arrive, flooding the control room and overwhelming the Daleks. The creatures continue firing, hitting several Thals including Kristas, but there are just too many of them now.

Ganatus attacks one Dalek from behind and sends it hurtling forward. It crashes into the main instrument bank. As the countdown reaches 4, there is a huge explosion and the countdown ceases. The lights in the control room dim considerably. Ian joins the Doctor, certain that they have succeeded in putting the Daleks out of action. Sure enough, most of the Daleks have stopped moving around. Only one still speaks, its voice slow and slurred. Susan and Barbara tend to Kristas' wounds while the Doctor goes to examine the Dalek.

The Dalek haltingly orders the Doctor to stop the power drain or else the Daleks will die. But the Doctor says he could not, even if he wanted to. Whether or not he wants to is a mystery. The Dalek's voice fades and its arms slump. Soon all of the creatures are completely motionless.

Alydon is disgusted by the loss of lives, both Thal and Dalek, but he is glad to see the true end of their conflict with the Daleks. The Doctor is worried about radiation leaks in the reactor and wishes to look at them. Ian stops him and hands him the fluid link which he recovered during the chaos. They will soon be able to leave this planet.

Alydon goes to Kristas' side to make sure he is all right. Susan and Barbara help him up. Alydon looks around at all the Dalek machinery, now abandoned. He can see no purpose for it all, but Barbara and Susan can: the Thals can adapt the Daleks' artificial sunlight technology and grow their own food. Ganatus agrees, but wishes there had been some more peaceful means of obtaining the technology. The Dalek casings all around them stand silent witness to the sad remains of this war.

Sometime later, the entire group is back at the Thal encampment in the petrified jungle. Much of the Dalek equipment has been brought back with them. The Doctor is helping to point out which items are useful and which are not. Alydon is amazed at the breadth of the Doctor's knowledge. For his part, the Doctor envies the Thals' opportunity to rebuild a whole world, but refuses an offer to stay and help. He seems to wish to try and get home but says little about it. He says he is too old to be a pioneer again, but believes that the Thals will succeed. The soil here is not as barren as he first suspected. The Doctor suggests that he might come back and visit Alydon's grandchildren in the future.

Susan arrives wrapped in an enormous Thal cloak, a present from Dyoni. She twirls and falls, eliciting giggles from everyone. Ian is ready to go, but the Doctor has still to fit the fluid link. There is no time like the present. Ian bids goodbye to Dyoni, Alydon, and Ganatus. Susan does the same. The Doctor teaches Alydon the Earth custom of shaking hands as he says goodbye. The three travellers enter the TARDIS.

Barbara, however, lingers with Ganatus. A bond has developed between them during their adventures and she is reluctant to leave. Ganatus presents her with some beautiful cloth with which she can make a dress. From his tone, he would very much like it if she would stay and model the dress for him. He starts to tell her what he wishes, but then is interrupted by Susan who calls for Barbara from the TARDIS. Ganatus kisses Barbara's hand, she his cheek, and then she is gone inside the TARDIS.

Alydon and Dyoni comfort the grieving Ganatus and all watch as the blue box fades away with a grinding engine noise. Dyoni is stunned by this, kneeling to examine the ground where the TARDIS had been, a look awe in her eyes.