The Doctor and Jamie lead a bewildered Victoria into the TARDIS console room. As many before and after, she is stunned by the hugeness of the ship's interior. The Doctor tells her the TARDIS is his home as he busies himself at the controls. He explains that the controls guide their flight through time and space. It is a "rather special version" of the time travel technology her father and Maxtible were working on. Still concerned about the nature of time travel, Victoria tries to work out how old the Doctor is. He concludes that - in Earth terms - he must be about 450. She looks askance and even Jamie is concerned at this. An embarrassed Doctor changes subject, pointing out that Victoria's large skirts might be impractical for adventuring.

Jamie leads Victoria off to choose a new wardrobe, admonishing the Doctor to try for a smooth takeoff so as not to scare Victoria. Somewhat stung, the Doctor activates the controls and the TARDIS dematerialises from Skaro.

Far out in the universe, on the barren rocky surface of a planet called Telos, an archaeological expedition is in progress. A group of scientists and astronauts are preparing to blast away at the side of a mountain. However, they are delayed when a member of their party - a soft-spoken giant of a man called Toberman - is not in position. In fact, he is still on the mountain. Professor Parry, the leader of the expedition, shouts him down impatiently. Toberman returns to the side of his mistress, an exotic woman called Kaftan.

All of the scientists and astronauts seem on edge. Clearly much is riding on this expedition and much danger attends it. Captain Hopper, a no-nonsense man in charge of the flight crew, thinks it all daft and is only doing his job. Parry believes that they have located the entrance to the "city of Telos" behind the rockface. Shortly, the blast echoes through the rarefied atmosphere and the rock is blown away. However, it is only after the dust settles that the group can see their objective - a pair of giant metallic doors set into the mountainside. The group whoops and cheers and races up the mountain.

They stare in awe at the giant doors for a moment. They seem somehow oblivious to the two images adorning the walls on either side of the door - crude renderings of what are clearly Cybermen in shining metal plate. Kaftan is first to speak, offering 50 pounds to the first person to open the doors. Parry starts to protest at this latest usurpation of his authority, but one of the astronauts steps forward to claim the money.

The man grabs first one of the handles - several inches above his head - and then the other. The crackle of electricity fills the air and the man jerks and falls. He is dead. The group is stunned, unsure what happened to him. Suddenly another noise echoes around the mountain. It is a laboured engine noise, rising and falling. Something has arrived just beyond their sight around a large outcrop of rock. Unbeknownst to them, it is the TARDIS.

Captain Hopper and his remaining crew - Callum and Rogers - along with scientist Haydon draw their guns and move forward. They are first to catch sight of the unlikely trio of newcomers as they circle the rock. Hopper addresses them at gunpoint. With no other choice, they come forward and join the expedition at the doors.

Jamie is incensed at the reception and is belligerent, but the Doctor moves off in a different direction completely. He spots the dead man and moves to examine him. Suspicion is rampant in the group. A cool-looking middle-aged man called Eric Klieg accuses the Doctor of having some part in the crewman's death, but the Doctor quickly refutes this. He sizes up the situation quickly, blaming an electrical booby trap in the doors.

Parry's assistant, Viner, believes the Doctor and his companions to be a rival expedition to Telos, searching for the same thing. The Doctor will neither confirm nor deny this and demands to know what Parry and his group are searching for. Parry and Viner explain they seek the last remains of the Cybermen. They died out centuries ago for unknown reasons, but it is believed they retreated to Telos, their home, to die. The Doctor takes this all in.

Meanwhile, Hopper is convinced that the expedition is over. One of his men has died and there is not enough money in the world to make the job worthwhile to him now. Parry seems to agree. Hopper and his men bear their crewmate back to their rocket where they will await the scientists as they prepare to leave.

But the Doctor is now resolved to continue the expedition and enter the city, despite Klieg's insistence that the Doctor and his "colleagues" leave at once. But the Doctor cannot leave, now that "that name" has been uttered. Cybermen. His determination shows in his eyes and his voice. Besides, as Jamie points out, they have as much right to be here as the others. Parry agrees, despite Klieg's continued protests.

There is clearly a strong antagonism between Parry and Klieg. Klieg and Kaftan are here "on sufferance only". They are not archaeologists and despite the fact that Kaftan's money is financing the expedition, she and Klieg have no say in the running of it. The conflict threatens to escalate between Parry and Klieg but Kaftan intervenes - smooth as silk - and defuses the situation. Parry is in charge.

The Doctor has observed this closely and now decides to go into action. He approaches the giant doors, preparing to open them. He attaches a small electronic device to the door and observes its reading. Then he impulsively grabs one of the handles. A gasp echoes round the group. They are certain he is going to electrocute himself. He seems pleased with the reaction, assuring the others the doors are perfectly safe. As he grabs the other handle, nothing happens and all are surprised. But neither do the heavy metal doors open. It is beyond the Doctor's strength to open them.

Jamie moves forward to give it a try, heaving with all his might. But he too is not strong enough. He blames a lack of exercise!

The Doctor, however, has found the most suitable candidate - Kaftan's servant Toberman. He is tall and muscular and perfectly fit. Kaftan opposes putting him in danger but Parry believes this is just the sort of contingency for which he was brought. The Doctor puts the icing on the cake by suggesting Toberman might be scared. The giant moves quickly forward, brushing past the Doctor on his way to the door.

It takes all of Toberman's strength, but the doors at last open and the way is clear to the gloomy interior. Klieg is all ready to enter, but the Doctor urges caution. The electricity may be off but there is still much to worry about. Klieg doesn't care and starts to lead the way in, only remembering at the last minute to let Parry - the leader - go first.

The Doctor wishes to follow the group, but Victoria is frightened and hangs back. The Doctor tries to distract her by complementing her new dress, but she thinks it is too short. He makes her laugh by pointing out Jamie's hemline and her tension eases. Victoria - still reluctant - eventually goes along with the Doctor and Jamie.

The group emerges into a control room, large and echoing and very dusty. At its centre is a control panel with numerous levers and labeled with logic symbols. Before the panel is a large clock-like dial with more symbols and an arrow pointer. There is a short set of steps on the other side of the room which lead up to a large hatch. It is firmly closed but clearly leads downward to some lower level. A table with four stools is off to one side. More of the bas-relief Cyberman heads adorn the walls, staring blankly down at the group.

Parry, Viner, and Haydon are quick to examine control panel. It is dark and dead. Klieg, Kaftan, and Toberman stand off to one side, conspiring quietly. Kaftan is worried about the presence of the strangers and orders Klieg to keep an eye on the Doctor. She clearly has a very strong influence over him and he agrees. She will watch Victoria and Toberman will watch Jamie. She must specifically warn Toberman to watch and not harm the lad.

The Doctor and his friends arrive and the Doctor quickly begins his investigations... with the walls. He announces - correcting Professor Parry - that there are two doors hidden in the walls. He also manages to open both doors by operating a "simple O/R gate" with the levers on the control panel. The archaeologists are excited by this development but Klieg wants to know how he figured all this out so quickly. The challenge in his voice is clear. The Doctor credits it to his own special technique: "keeping his eyes open and his mouth shut". Klieg is stung.

Parry moves on, dividing the group to more easily explore the different rooms. He tries to leave the women behind, but Kaftan won't hear of it. She and Victoria, along with Toberman, join Viner. They will explore one of the doorways the Doctor discovered. Jamie and Haydon will explore the other. The Doctor, Klieg, and Parry will stay here. Parry tells them to return before dark so they can return to the ship before the temperature drops.

As the groups leave, Parry turns his attention to the large hatch in the control room and begins looking for a means to open it. This time, the Doctor steps back to let Klieg have a crack at it.

Viner, Kaftan, and Victoria find their passage leading to a bright room full of instruments and wires. On one end is a pallet with a humanoid-shaped impression in the centre. The Cybermen clearly lie in it for some reason and there is a door - now open - which can be enclose it. In the centre of the room is a tall projector with much wiring which points at the pallet. On the other end of the room is the control panel, patterned after the first. As the group explores, Viner notes the absence of Toberman. Kaftan has sent him back as they "have Viner to look after them".

Viner begins to make notes of everything, but the women are more hands-on in their investigation. The curious Victoria climbs into the pallet while Kaftan tries to make sense of the controls. She deduces that the room is for recharging the Cybermen, the projector used to feed them with a sort of neuro-electric potential. Viner agrees. Victoria ignores Viner's pleas to get out of the pallet but Kaftan appears to welcome the meddling. She seems to be trying to activate the controls in a deliberate sequence as she watches Victoria over her shoulder.

Jamie and Haydon's passage leads to a totally black room with only a small bank of controls in one corner. Jamie listens for only a moment to Haydon's confusing explanation of the rooms alpha meson phosphor lighting system before he is distracted by something on the floor. It appears to be a sort of segmented metal caterpillar with large eyes and antennae. He is amused by it but Haydon is concerned even though the creature appears to be totally dead.

Klieg's preliminary investigations have yielded the rudiments of the logic system that should open the hatch, but the panel is still inactive and the hatch is closed. As the men focus on their task, no one notices Toberman emerge from the passageway and leave the complex via the main entrance.

The Doctor tries to talk Klieg out of continuing, saying that there are some things that should be left undone, even if they can be easily done. This leads to an argument over the difficulty of cracking the logic codes. Klieg is convinced it is very difficult and purposely so to protect the Cybermen's secrets, but the Doctor cannot resist pointing out the pompous mathematician's errors and lack of understanding. Unfortunately, these clues lead Klieg to the answer he has been seeking.

Suddenly the control panel - and indeed the whole complex - comes to life with a burst of power. The panel and the clock-like dial light up and the pointer moves. Klieg is triumphal. A rumbling of energy and machinery can be heard and felt all over. The Doctor is horrified, worrying that perhaps the Cybermen aren't quite as dead as first thought. He hurries off to check whether the others are all right.

In the recharging room, the surge of power is palpable as well. The controls light up and Kaftan reacts quickly. She moves a series of levers which activates the recharging equipment. The lid of the pallet slams shut, trapping Victoria inside before she can even move. Viner suspects this was no accident but worries more about Victoria. Brute force will not open the lid. Kaftan wonders aloud if they are already too late to save the girl.

In the other chamber, Jamie is startled when he sees what he thinks is a movement from the metal caterpillar, but Haydon thinks he's seeing things. He is more interested in the control panel which has suddenly become active. Jamie warns him to leave it be, but Haydon won't listen. At first nothing happens but then the lights in the room dim and a series of pulsating lights appear on one wall. It forms a shifting set of psychedelic patterns and Jamie stares at it as if mesmerised.

Viner has turned his attention to the control panel in an effort to save Victoria but he is too afraid of worsening the situation to touch anything. Logic escapes him in his panic. Kaftan establishes that Victoria is still alive by rapping on the lid of the pallet. She receives repeated raps in response. Relieved, Viner decides to go for help, leaving Kaftan to watch over the situation.

Once she is alone, she decides to finish the job she started. She moves more levers on the control panel and the projector in the centre of the room comes to life and a new hum of power fills the air. It appears that she will succeed in eliminating Victoria, but she is startled from her task by the return of Viner with the Doctor in tow.

Kaftan tries to activate the final sequence while the Doctor's attention is on the pallet, but somehow he sees this and warns her away. He joins her at the control panel and begins to reverse the logic sequence, Victoria's safety uppermost in his mind.

Haydon, too, is transfixed by the pulsating shapes on the wall, but with sheer force of will he breaks the spell and regains himself. He tries to pull Jamie away but cannot. The lad moves as if hypnotised toward the wall, almost into the shapes. Haydon manages to deactivate the controls and the shapes fade and the lights return to normal. Jamie regains himself, almost oblivious to what has happened.

Both men think it unlikely the Cybermen would need a hypnotising machine. Haydon believes the shapes are a target of sorts, with a subliminal centre that soldiers would be trained to see in the shapes. He has heard of something similar before and wishes to explore it further. Haydon instructs Jamie in the control sequence to use and he himself will watch the "target" when it appears.

The Doctor believes he has found the correct sequence of controls to release Victoria and he instructs Viner to stand by at the pallet. Kaftan he only wants to stand back. He is very aware of her part in this "accident". The Doctor is successful as the pallet lid swings open and the projector shuts down. He joins Viner and helps out a sobbing and gasping Victoria. The terrified girl clings to him.

The Doctor warns her to be more careful in future, but his comments are directed toward Kaftan as well. He bustles Victoria out, planning to go and check on Jamie next.

Meanwhile, Klieg and Parry continue their efforts to open the large circular hatch in the control room, unaware of the travails of the rest of their group. The tombs of the Cybermen must be below and the expedition will be a failure if they cannot be explored. Klieg blames the Doctor for his continued inability to open the hatch, convinced he knows more than he's said. This makes Klieg even more determined to succeed on his own. There also seems to be far more than professional interest in Klieg's determination.

The shapes are now back on the wall of the darkened room and Haydon is watching them. But it seems inconclusive. There must be more to the sequence, Haydon reasons, and at his urging Jamie activates the last control - a large button.

The lights change again and a machine noise fills the room. An unseen set of doors opens along the wall with the "target" on it. The Doctor, Victoria, and Viner enter and take in the scene. The Doctor is horrified by this meddling and tires to find out what Jamie has done. The confusion in the room grows. The Doctor hurries to the controls, working with growing desperation to try and undo the control sequence. But he is too late.

From the new doors, a Cyberman emerges, weapon in hand. There is a blinding flash of energy and Haydon collapses with a scream, smoke pouring from his body.

The Cyberman slides back into the wall and the machinery hum slows to a stop. The lights return to normal. The Doctor examines the body and then quizzes a confused Jamie over just which buttons he pressed on the panel. Parry arrives, oblivious to what has happened. His reaction is cool indeed, in stark contrast to the hysteria beginning to grip Viner. He begins to rant about the building trying to kill them and about Cybermen emerging from the walls. All that Parry hears is that there was a Cyberman here.

The Doctor is still trying to solve the problem of how Haydon was killed. Everyone else assumes he was killed by the Cyberman they saw, but the Doctor knows that is not true. Haydon was shot in the back, from the opposite direction of the one he was facing. The only way to find out how is to reactivate the control sequence which Jamie reluctantly does. The Doctor urges the group to stand well back as the lights dim.

The door opens and the Cyberman slides out again. This time, the assembled group notices a hatch open in the far wall, facing the Cyberman. From it a barrel protrudes and a flash of energy burst forth, knocking the head off the Cyberman. Victoria screams.

The Doctor quickly deactivates the controls and the lights come up, but this time the Cyberman remains in the open. He finds this to be a mock-up, a mechanical dummy with no human material at all. But its weapon is real. As is the weapon that destroyed it. He concludes that this is a weapons testing room, a place better left alone.

Viner and Jamie transport Haydon's body back to the control room while Victoria examines Jamie's "fossil" - the metal caterpillar. The Doctor is at her side, the sight of the creature triggering a memory. From his 500-year diary, he finds the creature is called a cybermat. While it is dormant, it is by no means a fossil and should be left untouched. Victoria, however, doesn't believe him and puts the creature into her handbag as soon as the Doctor's back is turned.

In the control room, Klieg and Kaftan have been left alone. Klieg has continued working on the logic code with no success. He seems rushed and Kaftan's badgering doesn't help. She is distracted when Toberman returns to the control room with a simple report: "It is done." Kaftan is pleased.

The rest of the group returns and Haydon's body is placed out of sight and covered with a coat. Klieg continues working while Kaftan receives details of the death. Parry - still cool and in control but grim-faced - calls everyone together for a meeting. Even Klieg is forced to stop and join them. Parry announces his reluctant decision to abandon the expedition and return to Earth at the next possible opportunity due to the death of the two men. Perhaps they can return to Telos when they have more men and equipment.

Klieg begins to protest but Kaftan stops him with a slight movement. The Doctor is the only one to notice. Just as Parry finishes, Captain Hopper bursts in, agitated and angry. He announces that none of them are leaving this planet. Some one - or some thing - has wrecked the ship's fuel pumps. The ship cannot leave now... and may never leave!

Some time later, as night falls, the necessity of staying in the complex weights heavily on them. Viner adamantly refuses to do so, insisting they all stay on board the rocket until the work is completed. But Captain Hopper puts paid to this. He and his men have 72 hours of round-the-clock work to do to fix the damage, and they have no time or space for the distraction of lodgers. He promises to halt work if his order is not complied with.

But there is another reason as well - Hopper is reasonably certain that one of the expedition members deliberately sabotaged the ship and he will not allow it to happen again.

Hopper leaves some warm anoraks and some food and returns to the ship. Klieg, back in business, attacks the logic codes again, determined to open the hatch and explore below. The Doctor tries to talk him out of it but is rebuffed. He is reminded that he and his friends can leave in their own ship whenever they'd like, but all three decide to remain.

The Doctor goes to "help" Klieg but is stopped by Toberman. There is a tense stand-off for a moment, broken when the Doctor comments offhandedly on Toberman's strength - adequate to do "a great deal of damage" if let loose in the right place. Kaftan seems to catch the undertone in the Doctor's voice - he knows or suspects Toberman's part in the damage of the rocket - and calls her servant off.

The Doctor moves to the logician's side and watches. Klieg is certain he has found the key - everything yields to logic - but is mistaken. His formula doesn't work but he is determined to succeed. He retraces his steps, thinking he has found the error. But unseen by anyone but Jamie, the Doctor changes the lever sequence and suddenly the great hatch opens. Klieg is very pleased with "his" accomplishment.

Parry is anxious to begin descending the ladder inside the hatch. When Kaftan refuses to let Toberman go, the Doctor refuses as well. He clearly wants to keep an eye on the giant. Kaftan relents with false graciousness. The Doctor takes a moment for a word of caution to Victoria before disappearing down the hatch. Then the women are left alone. Kaftan offers a ravenous Victoria some food, but when her chicken turns out to be a plastic-wrapped food cube, she is suddenly not hungry.

The group finds themselves in a tunnel far below the control room. Metal and rock alternate along the walls, and all is covered with a layer of ice. It is much colder than expected. They must explore quickly. A short walk brings them to an enormous central chamber. It is many storeys high and carved out of the rock of the mountain. Dominating it is a complex of cells stacked in rows which goes up as high as they can see. The cells are sealed by frost-covered transparent membranes and inside each one is a Cyberman, frozen forever in their tombs. The way it should remain, says the Doctor.

But Klieg seems to have other ideas. He goes to examine a control panel on one side of the room while Viner sets about recording everything in his notebook. He comments that it is too cold to remain here for long, but Klieg thinks he may find a way to hot things up, in more ways than one.

Back in the control room, Victoria is feeling drowsy even though she's barely touched her coffee. Unbeknownst to her, Kaftan has spiked her coffee with sleeping pills and they are working quickly indeed. Before long her head droops and her eyes close and she is asleep. After checking to make sure the girl is out, Kaftan goes to the control panel and closes the hatch. It clangs shut with a loud metallic finality.

The sound echoes in the tomb area. Jamie and Viner rush back to the foot of the ladder. Only Klieg and Toberman are not alarmed by this. The two men share a brief knowing look before Klieg returns to work on the control panel.

Viner returns with the bad news while Jamie remains on the ladder. Viner is nearly out of his mind with fear, certain they will all freeze to death down. The Doctor turns his attention to the calm Klieg, who says he thinks he's found a way to open the hatch from his control panel. The Doctor is very sceptical indeed.

Klieg activates the controls but Jamie reports no movement in the hatch. Only Klieg is looking the right direction to see the results of his actions - the tombs. They have started to thaw, very quickly. Klieg's face is alight with triumph. Shortly everyone notices as water begins dropping everywhere. All eyes are on the tombs as movement begins inside the cells. The Cybermen are coming back to life.

Parry is fascinated by the archaeological implications but Viner's nerve cracks and he throws himself at the controls, working them madly. He succeeds - likely by sheer luck - in reversing the process. The movement in the cells stops and the frost quickly reforms over them. Klieg is livid. Toberman holds the others back as Klieg draws a gun and aims it at Viner. Viner refuses to yield the controls and Klieg shoots him. Parry breaks free to go to him, but it is too late. Viner is dead.

Klieg restores the controls despite the outcry from Parry and Jamie. The Doctor is curiously silent. Klieg turns again to watch the unfreezing process.

Victoria awakes while Kaftan's attention is on the control panel. She notes the closed hatch and confronts Kaftan. Kaftan coldly tells her the hatch will remain closed "until we are ready". With much courage, Victoria pushes past Kaftan and reaches the control panel. She is ready to try anything to reopen the hatch and to help her friends.

Kaftan pulls a gun and forces Victoria away. She assures the girl that only Klieg's signal will open the hatch, according to their plans. Unseen by either of them, the cybermat in Victoria's handbag has suddenly come to life like its Cyber-maters and is inching its way out and onto the floor.

Jamie and the others have only now realised that Klieg had planned to find and reawaken the Cybermen all along. The Doctor has known it for some time. The only question left is why and Klieg is more than happy to explain. He belongs to the Brotherhood of Logicians back on Earth. They have a massive intelligence but no physical power. With the Cybermen allied to him, they will have the power to match their intellect. This is the only reason he and Kaftan financed the expedition and he is certain that as their resurrector, the Cybermen will ally with him.

The Cybermen are now fully active and beginning to break out of their cocoons. It is the greatest sight or the most terrifying sight ever seen, depending on your perspective.

In the control room, Victoria catches sight of the mobile cybermat and takes an involuntary step backward. She tries to tell Kaftan what is happening but she refuses to acknowledge this obvious ruse. Too late she sees a flash of movement as the creature leaps from the floor and onto her shoulder. Kaftan screams and struggles with it.

Victoria succeeds in tearing the Cybermat off Kaftan, but the woman is out cold. Victoria cannot make sense of the control panel and she decides that the best course of action is to get help from the spaceship.

In the tomb, all of the Cybermen are now free. They gather in a group before the central cell on the lowest storey. It is covered not by a membrane but a metal door adorned with the relief of a cyber-helmet. From the cell emerges a much large and more streamlined Cyberman. Its head is of a different shape and it seems to command respect and obedience from the other Cybermen. The Doctor calls it the Cyber Controller.

Parry is baffled by the Cybermen's detachment. The had clearly planned for their release and are now moving forward with no acknowledgement of their seeming "salvation". The Doctor realises it was all a trap - the means to reawaken the creatures always existed but could only be activated by creatures of a certain intelligence level, just what the Cybermen wanted. Now, as the Cyber Controller repeats, the "saviours" belong to the Cybermen.

Victoria returns to the control room with Callum and Hopper, begging them to help her open the hatch. She breathlessly explains what happened and Kaftan's part in sealing the men down below. Little do they know that as they all turn their attention to the complicated panel that Kaftan is no longer unconscious and is listening to them.

The Doctor, Klieg, Parry, Jamie, and Toberman are herded together whilst the Cybermen confer on the other side of the chamber. The Doctor refuses Jamie's suggestion to make a run for it and opts instead to address the Cyber Controller. He learns that the Cybermen submitted themselves to freezing because their machinery had stopped and their supply of spare parts had been depleted after the destruction of Mondas. That is why they attacked the moonbase some time later. The Cybermen have full knowledge of the Doctor and his part in both of these defeats. Not a calming piece of information.

The Cybermen are determined to survive no matter what. They plan to convert the captive humans into the first of a new race of Cybermen who will return to Earth and take it over. Parry is horrified by this thought, as is Jamie. He makes a run for it back down the tunnel.

He reaches the ladder and starts to climb but a Cyberman arrives and subdues him with a strange-looking weapon. Toberman, who has pursued Jamie, attacks the Cyberman but the mechanical creature's strength is too great. Back at the control room, the Doctor and the others are held fast by the Cybermen, protesting loudly.

Meanwhile, Callum and Hopper have resorted to removing part of the control board in an attempt to make sense of the electronics underneath. Callum is reasonably certain he's isolated the switch that controls the hatch and is ready to activate it when Kaftan springs to her feet. She holds the gun she had dropped in her struggle with the cybermat and uses it to force the others away from the control panel.

As she moves with them, Kaftan feels something near her foot. It is the cybermat and she remembers what happened before. Victoria seizes the moment and screams. Kaftan is distracted by her fear. The two men rush her and take the gun away. Callum holds her at gunpoint while Hopper at last operates the switch to open the hatch. To Victoria's great relief, it opens.

However, no one is waiting to emerge and there is no sign of anyone at the base of the ladder. The men have been gone for over an hour. Hopper decides that he has to go down and take a look. He grabs a couple of smoke bombs from Callum and heads down. Victoria is left above once again, angry at the rampant sexism she is encountering on this adventure.

With their captives firmly under control, the Cybermen complete their conference and announce their decision. Klieg is singled out to be the leader of the new race due to his status as a logician. He is proud of this honour...until he realises that this means he will be "altered". The Cybermen plan to eliminate the hindrance of fear from his brain but Klieg only knows he will no longer be human and he is terrified. So is Parry when he is designated to be the next. They will all eventually become like the Cybermen.

In the tunnel, Captain Hopper overhears this conversation and shudders. He starts to prepare the smoke bombs, knowing he's got to work fast.

The Cyber Controller has his soldiers prepare the tombs to freeze the humans until they can be processed. This prospect strikes terror anew into Jamie's heart and he cringes. Suddenly smoke bombs begin exploding all about and chaos erupts. Hopper urges the captives to run while the Cybermen try to regain their bearings.

In the confusion, the party is scattered and has trouble reaching the ladder. The Doctor and Hopper help them on their way and soon they are climbing out - all but Klieg and Toberman. Klieg appears to have taken a wrong turning and Toberman is set upon by the Cybermen. He struggles with them and proves a mighty adversary. One of the Cybermen raises his arm and a spark leaps from his hand to Toberman's head. It takes two powerful bursts before he finally goes down, but he is eventually subdued. The Cyber Controller sends him off to be "prepared".

Jamie and Parry are first out of the hatch, followed closely by the Doctor. However, he is grabbed by a Cyberman who tries to drag him back. Hopper and Jamie try to haul the Doctor out while the Cyberman tries to climb over him. Victoria hits the Cyberman's arm with the coffee flask and eventually it loosens its grip. The Doctor scrambles out but Victoria is grabbed. Callum activates the closing mechanism and the hatch begins to close on top of the Cyberman. It must eventually let go of Victoria to fight the heavy lid coming down on it. But it is not strong enough. The hatch closes and the Cyberman is left below on the ladder.

The Cyberman pounds on the hatch from below, making some mighty dents. Everyone in the control room holds his breath. Shortly the pounding stops and they can breathe again. The hatch has held. Jamie comforts a frightened Victoria and the others realise that Klieg and Toberman are still down there.

In the tombs, the Cyber Controller orders guards to watch the passageway in case the humans try again to come down. As the guard takes up a position, Klieg slips past and scrambles up the ladder. He is nearly out of his mind with fear. He knocks on the hatch, very softly, watching over his shoulder to make sure he is not heard.

In the control room, there is disagreement over the knocks. The Doctor concludes it must be Klieg and decides to open the hatch. He is much more dangerous down there than up here. Callum opens the hatch and Jamie and Hopper stand by to attack any Cybermen that might pop out. Klieg shoots out of the hatch and collapses on the floor. The hatch is shut tight.

Klieg reports Toberman's capture but seems to care little about him. The Doctor hopes Klieg has learned his lesson about trying to ally with the Cybermen, but it is clear that he has not. All Klieg wishes for is a stronger bargaining position. Hopper and the Doctor know that this dangerous person must be locked away for the safety of them all. Klieg and Kaftan are put in the testing room. It has only one door and they cannot escape, even though the door cannot be locked. Everyone feels better when they are gone.

Hopper is ready to return to the ship and complete the repairs. He still orders the others to stay off the ship but he does allow Callum to remain in the complex. Hopefully, nothing more will be heard from the Cybermen.

However, the Cybermen are hatching up a new plan. The break out several of the small bug-like metallic creatures - the cybermats. He orders them activated and wishes them tested on Toberman's brain. However, they are dormant from lack of use and require some further work.

In the testing room, Klieg sleeps off his recent harrowing experiences. Kaftan, however, is busy examining one of the cyberguns which were being tested in the room. It is wired to the hand of the mock-up Cyberman and she is trying to release it. Klieg wakes up and joins her, making sure the power is off before beginning work. He is soon able to free it and she believes that it will still work. If so, he can use it to attack the others and gain power over them.

Meanwhile, work on the cybermats is completed. They are set loose again and under the control of the Cyber Controller, they zoom in on Toberman's brain. He is spread-eagled on the floor and is at the mercy of the creatures. He is frightened half to death.

Klieg tests the gun, which fires the first time and burns a large hole in a nearby wall. The small x-ray laser is just what they need. But there is some hesitancy on Klieg's party. He is confident he can take command of the archaeological party but he balks at trying to bargain with the Cybermen again. For all his earlier talk, the presence of the mighty Cybermen was very frightening indeed. But Kaftan will have none of this. She has not sunk all her money into this venture to lose the goal because of Klieg's fear. She appeals to his ego and reminds him of the power of the gun.

This works and soon Klieg is preaching his invulnerability and impending mastery over the Cybermen. He is lost in his daze of power and logic. Kaftan snaps him back, reminding him of the work yet to do. Klieg is all too ready for that work. His first target will be the Doctor...

The Cyber Controller relents and calls off the cybermats. He seems almost disgusted by Toberman's display of fear. This the Cybermen will fix. The cybermats are placed on chutes and sent upward toward the control room.

In the control room, the group sleeps, exhausted after their adventures. Only Victoria is still awake on guard duty, holding Kaftan's pistol. The Doctor stirs and wakes and notices that Victoria should have woken him half an hour earlier. Victoria says shyly that she thought he needed his sleep, being 450 years old! He sits and chats amiably with the girl about her new place on the TARDIS. She says she is happy but misses her father. The Doctor understands, saying he misses his family too. They "sleep in his mind" and he can see them whenever he wishes, as she can do with her father. He cheers her up by reminding her of the unique adventure they are on and all the amazing things she'll be able to see and do.

Victoria goes off to settle in for her rest, but it's not long before the Doctor is shouting a warning to them all. The cybermats have arrived, crawling like bugs all around them. One of the creatures leaps up onto the chest of the sleeping Callum. The Doctor urges him to stay still while the others leap up. The Doctor approaches carefully and manages to swat the cybermat away. Callum gets up as the cybermat rights itself on the ground.

The group tries to make a dash for the recharging room but turns to face more of the creatures. The same things happens at the main entrance. They are well and truly trapped. Callum tries using his gun against the creatures but it takes many bullets to bring down just one of them. There is no time for that.

The Doctor comes up with an idea. He begins stringing large electrical cabling from the control panel out in front of them. He activates the controls and a hum fills the room. The cybermats surround and approach the group clustered round the control panel, but when they approach the cables, they begin to smoke and move erratically. Eventually they all give out distressed mechanical signals, belch smoke, and then cease functioning, killed by the electricity which scrambled their brains. The Doctor calls it "a complete metal breakdown"!

Klieg's aim is off and he hits Callum instead, a glancing blow to the shoulder. Klieg says it was deliberate but that is hard to believe. However, none of that matters. Klieg is now in command. While Victoria tends to Callum, Klieg reopens the hatch. He is convinced he can now bargain with the Cybermen, despite the Doctor's warnings. Klieg calls down the hatch for the Controller.

Down below, the Controller sends a majority of the Cybermen back to hibernation to conserve vital energy. The others release Toberman, who has now been "prepared". He looks the same at first, but his eyes are blank and there is an occasional flash of sliver beneath the cloak he now wears.

The Controller and Toberman climb the ladder, but Klieg stops them at the top with his gun. He tells the Controller he will allow him to be revitalised if he agrees to an alliance. The Controller agrees to listen, his voice somewhat slower due to the power loss. Kaftan orders Toberman released and the Controller does so, but only after an unseen telepathic conference. Toberman follows Kaftan's orders to guard the Doctor and the others. Jamie notices the subtle changes in him, as does the Doctor.

Klieg's deal is simple: the Cybermen must agree to aid him in the conquest of Earth. Parry is stunned by this revelation. The Doctor is not. The Cyber Controller agrees and is allowed to go to the revitalisation chamber. Klieg forces Jamie, Parry, and the Doctor to go with him. Victoria is held back as a hostage to assure that they will assist the Controller.

Both Klieg and Kaftan order Toberman to close the hatch but he does not obey. His mistress is angry but not suspicious.

In the recharging room, the Cyber Controller tries to climb into the pallet but is too weak to do so alone. Jamie and Parry are content to let him exhaust himself but the Doctor has other ideas. He actually helps the creature get in. However, when he activates the controls, the pallet lid slams shut and they understand. The Doctor has trapped him there, but the revitalisation process has already begun. The Doctor plans to make sure the Controller stays in there no matter what.

In the control room, Victoria tries her best to sow concern among her captors. She tries to elicit fear of the Cybermen, but that doesn't work. Klieg believes his cybergun is protection enough. However, when Victoria says she saw a gun like that in the recharging room, Klieg and Kaftan become worried. A fully-revitalised Cyberman with a weapon would be a threat indeed. They are now too worried to even go inside the revitalisation room.

Jamie has secured the pallet lid with ropes and he is confident the Controller can't get out, no matter how strong he is. The group is surprised when the revitalisation sequence ends of its own accord. The silence is deafening. It is also short-lived. With a few mighty blows, the Cyber Controller smashes through the pallet lid and is quickly free of Jamie's trap. They all back away and let the Controller out. He sends a message out to Toberman on the other side of the door.

Klieg puts Toberman on the door to watch, not realising his allegiance to the Cybermen. He and Kaftan start to explain to Victoria and the recovering Callum how the logicians plan to build a better Earth under their leadership. No one notices Toberman leave his post at first. By the time Klieg does see it, it is too late.

Toberman raises his arm, encased in metal and plastic like the Cybermen, and smashes it down on Klieg's head. He stands obediently by when the Controller emerges, tall and very powerful. Kaftan is horrified by what has been done to Toberman and demands to know why the Controller has broken his promise. Promises "have no value" to Cybermen. Their will is all that matters.

The Controller opens the hatch and turns to go. However, Kaftan boldly closes it before he can reach it. Defiant, she produces a pistol and fires several bullets at the Controller. They have no effect and she is now trapped with no place to run. The Controller has picked up Klieg's cybergun and now fires it at Kaftan. She collapses in a smouldering heap, dead. Victoria screams.

Toberman is stunned by this. His mistress has been killed by the Cybermen. He is only partially converted and deep in his brain he remembers Kaftan's kindness to him. His face registers confusion. As the Controller steps to the control panel to reopen the hatch, the Doctor goes to Toberman to play on that confusion. He reminds Toberman he is a man, not a machine. He is human. He must avenge Kaftan's death and help the others.

As the Controller turns to call down the hatch, Toberman moves into action. He overcomes Cyber-control and attacks the Controller, his anger more than a match for the Controller's strength. The struggle is fierce, but eventually Toberman gains the upper hand. He picks the Cyber Controller up and flings him against the control panel. He and the panel explode. The Controller lies face down in a smoking heap.

Two more Cybermen start to climb through the hatch. Jamie grabs the cybergun and uses it to despatch them. They fall back down the ladder with the clatter of metal. Jamie is convinced they've put an end to the Cybermen but the Doctor is not certain. He must go back down to the tombs to make sure.

Jamie volunteers to go with him, but the Doctor chooses Toberman instead. Jamie needs to stay here and look after Victoria. The Doctor takes a moment to reinforce Toberman's mastery over Cyber-control but it is hardly necessary. He knows the silver giants are evil and must be destroyed for what they did to Kaftan. The two men head down the hatch, the Doctor refusing to take the cybergun offered by Jamie.

Callum groans and Jamie, Victoria, and Parry go to him. Unseen, Klieg has regained consciousness. He gets up silently, snatches up the cybergun where Jamie has left it, and climbs down the hatch.

The Doctor and Toberman reach the tombs without incident. The Cybermen are all inside, dormant but not frozen. Toberman wishes to smash all the equipment, remembering vividly what was done to him, but the Doctor stops him. They must use the equipment to refreeze them. He sets about doing so.

However, Klieg bursts in and forces the Doctor away from the controls. He reverses them and waits for the Cybermen to re-emerge. The union between Cyber-power and mass intelligence will create a supreme power for Earth. He will be the new Controller.

Jamie has followed them all down and tries to attack Klieg during his rant, but Klieg catches him and forces him at gunpoint to join the Doctor and Toberman.

Suddenly the Doctor seems to grasp Klieg's idea for world domination. He goes on and on about the brilliance of Klieg's plan. Klieg's own mind will be the pattern for everyone's way of thinking. The new world will consist only of Klieg's own thoughts. This flattery works and Klieg acknowledges the truth of the Doctor's statements. He invites the Doctor to join him but it was all a ruse... just to find out how mad Klieg really is!

Hopper arrives from the ship, announcing that it is fixed and ready to take off. Victoria and Parry care little. They listen carefully at the hatch for any sign of their friends below. It is all that matters to them now.

Klieg, stung by the Doctor's taunts, decides to kill him. Jamie joins in, further angering the mad logician. However, he decides not to kill them himself, preferring to give them over to the Cybermen for conversion. One of the creatures approaches and Klieg goes to join it - his new ally.

Suddenly the Cyberman whips out its arms and throttles Klieg where he stands. Cybermen do not make deals. Klieg is dead and the Cyberman turns on the others. Toberman goes into action and struggles with the evil creature. The fight is short but intense. In the end, Toberman rips open the creature's chest unit and foamy gunge spills out. It dies writhing in agony on the floor. Jamie and the Doctor are horrified.

But there is no time to waste. The Doctor and Jamie reactivate the freezing controls and the Cybermen are once again placed in hibernation in their tombs. Hopefully forever.

The Doctor, Jamie, and Toberman climb up into the control room, much to Victoria's relief. The Doctor goes straight to the control panel and begins flipping switches. He plans to re-electrify the doors, but also the control panel and the hatch. Hopefully that will be enough to stop anyone entering here again. He hurries all the others out, although Jamie stays behind to look after him.

The process is brief and the Doctor is soon finished. All that remains to complete the circuit is to close the main doors. However, they are not safe yet. The Cyber Controller, badly damaged but still active, stands up and begins lurching toward the intruders. They are nearly trapped but by circling around him, the Doctor and Jamie are able to escape. They race for the doors with the Controller in pursuit.

They get outside and start to close the doors by hand, but the Doctor remembers the electrical trap he has built it. Jamie races to grab some timber with which to push, but they are not strong enough to hold back the Cyber Controller. Determined to see his race survive, he pushes outward on the doors to open them. He is stronger than the Doctor and Jamie.

Suddenly they are joined outside by another pair of hands - Toberman's. He is equally determined to keep the evil inside. As Jamie and the Doctor fall back, Toberman's will and strength triumph and he closes the doors at last on the Cybermen. Both the Cyber Controller and Toberman are electrocuted by the Doctor's trap and both are killed.

Outside, Parry is stunned by yet another death. He looks shell-shocked, far from his initially coldness. Captain Hopper urges him back to the ship which is ready to blast off in 9 minutes. After a regret-filled goodbye to the Doctor, he moves off. The Doctor and his friends head off to their own "flying machine" as Victoria calls it.

Jamie asks if this is really the end of the Cybermen and the Doctor says it is - although he says he doesn't like to make predictions!