A crowd gathers, anxiously awaiting the return of Lord Barset. He appears and greets the cheering journalists, expressing surprise at their enthusiasm and interest, given the fact that the 2012 Olympic Games are currently taking place elsewhere in the country. He acknowledges that without their support, and that of their readers and audiences, he wouldn’t be in the position he’s in today. Thanks to them and the awareness they’ve raised, the Commission has finally granted him a licence approving his planned visit to Antarctica to discover what fate befell his grandfather’s lost expedition in 1929. Through reading the expedition diaries, Lord Barset has felt a connection with his grandfather all his life, and this trip will give him the opportunity to pay his last respects to the lost explorers and lay their remains to rest.

Sometime later, Lord Barset’s expedition is underway in the Antarctic, but things are not going well. Professor Mark McIntyre has led a small exploratory group into the frozen wastes, but the main base has lost contact with them and Lord Barset is forced to lead a rescue party from The Fortitude to their last known location. In the distance they can see the dig site, but there’s no one around so they assume McIntyre’s team must still be working underground.

At that moment, McIntyre and the others are making their way through the treacherous ice caverns, using gigantic heat emitters to break away huge chunks of ice. Their last attempt has taken the ice back about ten feet and they’re racing to get the water mopped up before it freezes again. They still can’t see anything, but the sonic triangulation readings confirm there’s something buried inside. McIntyre’s French assistant Genevieve Marceau estimates it’s a cuboid object over two metres tall. The young Scottish crewmember Ben Hodgson calls them over to an area where the ice has cracked and he can see the object. Suddenly there’s a minor cave-in and everyone ducks for cover. When the ice settles, the team have a few bruises, but nothing more serious. Obviously they melted away more than they thought and the remaining ice must have shifted. The cuboid object is now exposed to the air and the team is amazed to see that it’s an old London police box - buried in ice that’s been here for millions of years!

The air is filled with a fluttering noise which throbs in synch with an electronic hum. The Doctor is frantically completing work on some equipment. He finishes the job just in time and then runs for his life down the ice tunnel. He screeches to a halt as he comes face to face with his enemy. To his horror, the enemy raises a weapon and prepares to open fire. The Doctor shouts an urgent warning, but it’s too late. The effect of the weapon causes the ice walls around them to shatter and the entire area is instantly flooded with water. Within seconds, both the Doctor and his enemy are floating motionlessly in the rapidly freezing water.

Lord Barset’s security team, headed by Captain Harman, arrive at the dig site. Harman tells his troops not to take any chances and they arm their weapons. Barset orders them not to fire unless he gives the signal. Then they prepare to enter the ice caves and see what ancient terrors McIntyre has unleashed.

Genevieve is confused by the police box, having never seen or heard of one before, but even though McIntyre has, he’s just as baffled as she is. She removes a key that’s sticking out of the lock and suggests trying to open the box, but just then there’s a commotion nearby as Lord Barset and Harman’s troops swarm into the area. They look ready to open fire, but Ben persuades them there’s no need for any hostilities. McIntyre is furious and demands to know what they think they’re doing. Barset points out that The Fortitude lost all radio contact with McIntyre’s team six days ago which was naturally a cause for concern. The Professor is forced to accept the point, but still feels there’s no need for such militaristic nonsense. Before they can argue further, Genevieve discovers something else - the probes are showing something even more incredible than the police box - it’s a body, frozen in the ice!

The Doctor is completely disorientated as his body gets dragged along by the current of icy water. He thought he was drowning, but now everything seems so still…

Back at their base camp, Genevieve and Ben join their colleague Bailey and organise the soldiers as they manoeuvre a huge block of ice through the doors and into the main laboratory. They wheel over some smaller heat emitters and Genevieve sets them to minimum so that as the ice melts they can gently wash away all the muck and sediment that was frozen with the body. They can’t see the figure in the ice very clearly so they’re not even sure whether it’s male or female, but they do know it must be millions of years old. Ben tells Genevieve that he’s on this trip because the money’s good, but he wonders what she and McIntyre were expecting to find. She admits to being in the dark about the expedition and thinks McIntyre and Lord Barset have their own agenda. Ben asks if she minds being left on her own with the man in the ice as he wants to start work on retrieving the police box and he thinks she looks a bit spooked.

In the ice cave, McIntyre demands answers from Barset. He was originally promised unusual artefacts and remains - not an impossibly preserved body buried in a layer of ice frozen millions of years ago! He’s an archaeologist, not a fool, and he realises Barset knows more than he’s telling. Barset regards McIntyre as a starchy old man who does things by the book and whose career had all dried up. The reason he chose McIntyre for this expedition was because he has a passion to prove himself. He’s brilliant, but was frustrated because no one was taking any notice of him any more. Barset points out that he saw the licence he’d been granted and knew there was no mention of archaeology, so he must have realised there was something cloak-and-dagger about this mission all along…but McIntyre still wants to know why Barset needed to bring along all the guns?

Back in the laboratory, Barset is eager to find out whether the body in the ice is reptilian. The question surprises everyone and Genevieve wonders exactly what he was expecting to find. She removes the sheet and reveals a perfectly preserved man underneath. The clothes have mostly rotted, but from the remains it looks like they were machine woven, which would be impossible. She’s also done a full medical scan and the results show that although he looks human in appearance, there’s very little that’s recognisable about his internal organs. With such an extraordinary level of preservation, there may even be some blood she can take for DNA analysis, but when she tries to take a sample, the man cries out in pain and sits up. It‘s the Doctor! McIntyre is amazed to discover the man can speak English. Lord Barset immediately radios Harman and orders him to bring a weapon to the lab straight away. McIntyre objects as the man doesn’t seem to be dangerous and Genevieve points out that he isn’t reptilian either, as Barset was expecting. McIntyre asks the Doctor who he is and how he got in the ice, but he can’t remember and complains about a noise in his head. Just then, Ben calls and says they’ve found something else in the ice cavern. McIntyre is furious that Barset allowed the work to continue without him, but Barset reminds him that he doesn’t need McIntyre’s permission. The archaeologist warns that unsupervised melting could cause flooding and result in potential damage to any further finds, so Barset orders him to return to the cavern and start supervising. He also asks Genevieve to stay behind and look after their mystery man - perhaps she can make him a nice cup of cocoa? As the others leave, the Doctor observes that her boss seems rather unpleasant. Unfortunately Genevieve has to put up with it as it’s his money that’s funding the expedition. When she tells him they’re in the Antarctic, he seems momentarily surprised that he’s back on Earth. He vaguely recalls the names Ace and Hex, although he knows he’s travelling alone now. He also remembers someone firing at him and blasting through the walls, then water flooding in. He asks Genevieve what year it is and when she tells him it’s 2012, he realises he’s been frozen in the ice for millions of years.

McIntyre storms into the cavern and orders Ben to turn off the emitters as they’re set far too high, but Barset tells him to leave them on. As Harman and his men start mopping up the water, they can see another twenty figures embedded in the ice. McIntyre wonders if this was what Barset was really looking for and asks him how much he knows. Barset finally admits that there was one survivor from his grandfather’s expedition back in 1929, but the family kept it secret because he’d gone stark, staring mad. He died a few days after being found, but he carried with him the expedition diary and Barset is the only person alive who’s ever read it.

The Doctor changes into some spare clothes and thanks Genevieve for the hot cocoa. He’s starting to warm up nicely, but then he hears a fluttering noise which throbs inside his head. It reminds him of something, but he can’t remember what. Genevieve asks how it was that somebody was firing at him millions of years ago, but before he can answer she gets a call from the cavern asking her to come down with her scanners as they‘ve discovered more bodies in the ice. The Doctor insists on coming with her and ignores her attempts to deter him by suggesting he may not be well enough.

The ice starts to crack at an increased rate so the Doctor advises them to switch off the heat emitters, but Barset isn’t interested in his suggestions. The Doctor hears the fluttering noise again and it seems to be getting stronger. He doesn’t know what’s causing it, but somehow he knows it’s important. Once again Barset orders Ben to take him back to the control room and this time the Doctor doesn’t object as he’s keen to have some more cocoa anyway. Then Barset asks Genevieve to conduct a full medical scan of the reptilian body, but to do this they’ll have to take it back to the lab. He’s still convinced that the contents of the cave will bring them all unprecedented wealth and power, a claim that surprises Genevieve.

The Doctor runs for his life down the ice tunnel. He screeches to a halt in front of his enemy who claims to have been betrayed. To his horror, the enemy then raises a weapon and prepares to open fire. The Doctor shouts an urgent warning, but it’s too late. The effect of the weapon causes the ice walls around them to shatter and the entire area is instantly flooded with water. Within seconds, both the Doctor and his enemy are floating motionlessly in the rapidly freezing water.

The Doctor comes to with a start. His recollection was different this time and he wonders about the enemy who claimed to have been betrayed. He looks around the control room and comments on how well equipped the base is - the satellite transmitter and batteries must be cutting edge technology. He wonders how Ben could have ended up working for such a stupid man and he admits that it’s just for the money. Ben thinks the Doctor has a friendly, honest face and is happy to put his gun down. For a moment, the Doctor wonders which face he has at the moment and is reassured when he looks in a mirror. Ben suggests he might want to be checked over by their doctor, although he’s back on their ship, The Fortitude, which beyond the ice barrier. The mention of a doctor triggers a memory for the Doctor and he suddenly remembers who he is!

Back in the ice cavern, Professor McIntyre is advising caution, but Barset tells them to ignore the Doctor‘s warnings as he’s clearly deranged. He gives orders for the other creatures to be melted out of the ice too, then they can move deeper into the cavern to see what else they can find. Genevieve is worried the creatures might come back to life like the Doctor, but Barset says it’s far more likely the man just fell down a hole into the ice a few days ago after losing his way. Genevieve reminds him that the medical scan showed the Doctor wasn’t human, but Barset insists that whatever his story is, it’s got nothing to do with what they’ve found here. He orders Harman to leave the emitters switched to full and then helps carry the reptilian body back to the lab. McIntyre has noticed that the other creatures in the ice are slightly different to the one they’ve recovered so far. The head of the first creature is of a different design and the build is much slimmer. Barset is critical of McIntyre’s inability to draw any conclusions from this, but the Professor reminds him he’s an archaeologist, not an expert in unknown species. Barset assumes the slimmer figure must be the leader and the others are ‘grunts’, who carry out the orders.

The Doctor finds out more about Barset’s purpose in coming to the Antarctic, but if this expedition was just about finding out what happened to Lord Barset’s grandfather, why did he bring McIntyre and Genevieve? Ben says he overheard the two scientists talking and they both knew they were here to find more than just bones from 1929. Not only did they bring high-tech equipment with them for probing, they’ve all been issued with weapons! The Doctor wonders if Barset is up to something illegal and asks Ben if he’d object to him contacting the authorities for help. Ben says he doesn’t mind him trying, but the radio’s been on the blink since they start digging here. He switches the radio on and all they hear the interference, but the Doctor can hear something else in the background…a fluttering noise which throbs in synch with an electronic hum! It’s the noise he’s been hearing ever since he woke up, but he knows he‘s heard it before. It’s the sound of sonic vibrations and they must be stimulating his brain, helping him to remember what happened all those years ago. And it seems to be getting louder…

In the laboratory, Genevieve and McIntyre prepare for the arrival of the reptilian body. She thinks the creature might be dangerous and asks the Professor if he knows what they’re getting themselves into, but before he can answer, the others arrive. They drag the ice block in and Genevieve conducts a scan which confirms that the creature doesn’t resemble the human form in any way. McIntyre insists on learning more of the secrets from the 1929 diary, but Barset refuses to disclose anything yet. If the Doctor is right about the creature coming back to life, they can get all the answers they want then. They both agree to question the Doctor further, but Genevieve reminds them he’s just come out of a coma that’s unprecedented in medical history and advises against any form of interrogation in case he suffers a relapse. Barset ignores her recommendation, but allows her to come along while Harman stays behind to keep an eye on the reptile. Once he’s alone, Harman contacts Kelly back at the ice cavern to check on how things are going. Unbeknownst to him, the reptile creature is slowly starting to come to life behind him. It makes a strange hissing sound as it struggles to breathe…

When Barset joins him in the control room, the Doctor greets him warmly and Ben explains that his memory has started to return thanks to the radio interference. Barset is furious with McIntyre for not telling him earlier that they’d been suffering from interference, but the Professor says he tried to tell him, but was ignored. The Doctor says he needs to get to the police box they found. He’s still not entirely sure why, but he’s confident he’ll know more once he’s inside.

In the lab, Harman briefs his team on getting some replacement batteries sent out from The Fortitude, but in the meantime he asks them to recharge the snowcat batteries. Kelly reminds him there was a weather warning just before they left and the storm will reach them in a few hours. Suddenly there’s a crash behind Harman - he leaps to his feet and sees the terrifying form of the ice creature standing before him. He warns the monster to stay away, but it knocks him to the floor as easily as if it was swatting a fly.

Genevieve asks the Doctor what else he remembers and he confirms that he really did get trapped in the ice millions of years ago and it was one of the other creatures that fired at him. He remembers drowning and putting himself into a coma to survive. Suddenly an alarm sounds, indicating that Captain Harman must be in trouble in the lab. They contact him by radio and he tells them the creature came to life and knocked him out. He doesn’t know where it’s gone, so Barset orders him to go and find it. The Doctor realises Barset must have deliberately wanted to revive the creature and asks him what he hopes to get out of it, but Barset refuses to answer his questions.

The creature from the ice makes its way through the tunnels in search of the cave where its colleagues are still entombed. It continues to hiss as it struggles for breath in Earth’s atmosphere.

Genevieve tells the Doctor that Lord Barset believes the creatures they found in the ice are the remnants of a species that pre-dates the emergence of the human race. At first Barset refuses to be drawn, but then he explains that his grandfather’s ship, The Rochester, sank without trace in 1929 and only one man got away, taking a diary with him. When he was found he was half frozen to death and driven mad by fear. He eventually died, still screaming about monsters. The Doctor points out that the creatures here have been frozen in the ice for millions of years, so they can’t have been involved in what happened in 1929. In the diary, Barset’s grandfather described the creatures as ‘lizard-men’, intelligent reptiles that walked upright and had superior technology. The Doctor realises Barset has come in search of technology! McIntyre says they’ve found no trace of the lost expedition and Genevieve adds that these ice caverns are quite some way from the map references they were originally given. They came to this location to investigate strange readings on their sonic probes and they just assumed the original references were off target. They hear further sounds of commotion and contact Harman back in the ice cavern. The radio signal is difficult to hear because of interference, but it’s evident that the team in the caves are in trouble. Barset and Ben arm themselves and go to investigate, ordering the others to stay behind. Genevieve realises the Doctor doesn’t think the creatures as the same ones Barset was expecting to find. The Doctor is starting to remember more and says the creatures are war criminals. He rushes off to follow the others, hoping to avert a massacre…

In the cavern, a full-blown battle is underway between Barset’s soldiers and the creatures from the ice, all of whom have now been fully revived and appear to be using some form of sonic weaponry. Harman says they’ve lost five or six soldiers already and their bullets just bounce straight off the creatures. Barset remembers they have a supply of grenades back on the snowcat, but before anyone can go to get them, the Doctor appears at the end of the tunnel and shouts out to everyone to stop firing! Surprisingly, it seems to work and the ice creatures lower their weapons. Genevieve arrives and warns the Doctor to be careful. The creatures obviously recognise the Doctor and their leader addresses him by name. Now he recognises them too and remembers the time when he last saw them…

The creatures had broken out of their cells and the Doctor went to Geldar to find out what happened. Geldar explained that the guards had betrayed them and he urged the Doctor to save himself before it was too late. The Doctor asked if they’d activated their distress signal, but Geldar told him the power had been cut. The Doctor sent him to the communications centre to switch the signal on from there while he tried to find a way to re-connect the power on his way back to the TARDIS. The Doctor completed work on the equipment just in time and then ran for his life down the ice tunnel. He screeched to a halt as his enemy appeared and raised a weapon. The Doctor shouted an urgent warning, but it was too late. The effect of the weapon caused the ice walls around them to shatter and the entire area was instantly flooded with water. Within seconds, both the Doctor and his enemy were floating motionlessly in the rapidly freezing water.

The The Doctor grabs Genevieve, McIntyre and Ben and drags them behind the nearby heat emitters where they can be shielded from the sonic vibrations, then he switches them on and turns them to face the Ice Warriors. The effect is instantaneous and the creatures start to back away in distress. The four of them are able them to escape, although Barset and Harman have to be left behind. The Doctor and the others emerge from the caves and find themselves on the ice-flow, exposed to the stormy winds of Antarctica. They can’t survive out here in the wilderness for long and the Ice Warriors won’t be far behind them. McIntyre leads them towards the team’s snowcat, Aristo 1, and they all climb aboard, with Ben offering to drive. In the cavern, Arakssor’s first officer Ssrongar manages to switch off the heat emitters, then he is ordered to find the escaping humans and kill them.

Ben has trouble starting the snowcat and admits that he’s only had a couple of goes at driving it, but eventually it starts and they race off across the ice. Some Ice Warriors emerge from the cave entrance behind them and open fire with their sonic weapons, but fortunately the group has already reached a safe distance. Arakssor orders Ssrongar to return to the prison as there’s a lot of work to do. In the cave, Harman is pleased to hear that the others escaped. Arakssor wonders where they could be heading and forces the humans to tell them about The Fortitude. He asks about their ship’s weapons capability and whether it could be used to attack them, but Harman assures them it can’t.

Aboard the Aristo 1, McIntyre tries to make radio contact with The Fortitude, but he’s unable to get through because of the electronic interference. Genevieve urges him to keep trying. The Doctor is frustrated because he can’t remember what’s causing the sound, but he hopes the effect must have a limited range and that it isn’t blanketing out the whole of Antarctica.

Barset explains that The Fortitude isn’t a military vessel, but Arakssor is worried it could still be used to bring other soldiers here to attack them. Harman realises Arakssor thinks they’re talking about a spaceship so he explains that it’s just a vessel for crossing the water. It only brought them as far as the ice-flow, then they travelled to this location using their snowcats. Arakssor asks how long it will take the Doctor to reach their ship and Barset estimates it’ll be a couple of days, but Harman reveals that the battery on Aristo 1 still needs replacing so it won’t get them to their destination, nor is there enough cold weather gear aboard. As there’s a storm approaching, it’s likely they will die!

To the horror of those aboard, the engine of the Aristo 1 starts to falter and the vehicle begins slowing down. They realise the battery has run out and they don’t have a replacement. Eventually they come to a complete halt. McIntyre tries desperately to contact The Fortitude again, but without success. They’re too far away to make it to the ship on foot and nobody even knows they’re here - except for the Ice Warriors. The Doctor hands out some additional clothing and when Genevieve points out there isn’t enough for all four of them, he reminds them he’s an alien life form and won’t need as much protection from the cold. Nevertheless, their only chance of survival is to get a signal through to the ship, so they need to get as far away as possible in the hope that the interference has a limit. They take the portable transmitter with them so that once they’re outside the influence, they can call for help. Ben whispers to the Doctor that they’re chances aren’t looking good and secretly the Doctor agrees, but it’s their only hope.

Arakssor orders Barset and Harman to use the heat emitters to melt the remaining ice inside the cavern, warning that if they show any sign of trying to use them as weapons against his men, Ssrongar will kill them. Barset wonders what else is hidden beneath the ice, but Arakssor refuses to answer. As they increase the power, Barset and Harman hear the fluttering, throbbing sound and realise it’s the same sound that’s causing the radio interference. As the ice starts to melt, they see another figure embedded inside and wonder who it is. Arakssor instructs Ssrongar to assess the condition of this planet, then locate their sonic cannon.

The Doctor, Genevieve, McIntyre and Ben struggle through the wind and snow, then eventually they stop to rest and try the radio again. Everyone seems to be bearing up reasonably well apart from the elderly McIntyre. They have no luck with the radio, so the Doctor suggests they continue their trek for another hour or so before trying again.

Barset and Harman can now see that the figure in the ice is another one of the Warriors. Harman is starting to wonder what will happen to them once they’re no longer needed, but Barset finds his attitude annoying. Ssrongar reports back to Arakssor and tells him this planet’s atmosphere is suffering from a build-up of gasses in the advanced stages of causing climatic upheaval. The mean temperature is rising, but extreme weather fluctuations are causing severe cold conditions and a freezing storm is about to envelop this continent. Arakssor is delighted and plans to exploit this phenomenon to their advantage!

McIntyre stumbles in the snow and the others rush back to see if he’s alright, but he’s in a bad way and tells them he can’t go on. They realise they can’t let him to go to sleep so the Doctor and Genevieve try to help him back on his feet, but he knows he’s only going to slow them down. The storm is getting worse, so he insists they go on alone. Ben tries the radio again and the Doctor studies the sound of the interference, desperately racking his memory for clues as to its origin.

Geldar tells the Doctor his people owe him so much, but he dismisses it as all in a day’s work. The elderly Martian is surprised that he treats the matter with such lightness, but he knows deep down that the Doctor understands. He also fears that it isn’t over yet and the thought of Arakssor’s vision for his people’s future still haunts him. The Doctor believes this is healthy - that way he’ll make sure it never happens again. Suddenly an alarm sounds. Geldar is horrified when he learns that Arakssor and his cohorts have broken out of their cells after the guards betrayed them. He urges the Doctor to save himself as Arakssor will show him no mercy. The Doctor asks if they’ve activated their distress signal, but Geldar tells him the power has been cut. The Doctor sends him to the communications centre to switch the signal on from there while he tries to find a way to re-connect the power on his way back to the TARDIS.

The Doctor finally recognises the sound - it’s the Ice Warriors’ distress signal. Genevieve has been unable to wake Professor McIntyre, but Ben thinks he may be the lucky one.

Arakssor congratulates the humans on breaking their way through the ice into his ship’s communications centre. He reveals that the figure they released from the ice is Geldar, a former opponent who is now at Arakssor’s mercy. As the elderly Martian starts to revive, Barset asks Arakssor about the fluttering, throbbing sound they keep hearing, which prompts the Warrior to switch it off.

Out on the ice, the Doctor realises he can no longer hear the interference. He orders Ben to try the radio transmitter again, but the young officer is too despondent to even try. Even Genevieve tells him not to waste his time as they haven’t moved since their last attempt. The Doctor urges Ben to do it as it needs to be a voice that the crew on The Fortitude will recognise. Ben agrees and is amazed when he gets through to the ship!

An Ice Warrior reports to Arakssor and assures him the transmitter strength of the distress signal was very weak and there’s no record of any response being received. Arakssor turns his attention to Geldar and explains that they all owe their reawakening to the humans, the dominant race that emerged on this planet while they were encased in ice for millions of years. Geldar is pleased that his people have been free of Arakssor’s madness all this time, but this infuriates Arakssor who believes his race have been living the lives of cowards instead of ruling as masters of the galaxy. He accuses Geldar of being a traitor, but the old man says he just wanted peace and co-existence with others. Geldar pays his respects to the Doctor for his help in preventing Arakssor’s military coup, but Arakssor doesn’t recognise the authority of the old court. He believes his ideals will have lived on and he plans to return one day to Mars to reclaim his empire - but first he must make a fortress of this world. His first act is to kill Geldar. As the old man falls to the floor dead, Arakssor tells Ssrongar they will use the recently recovered sonic cannon to alter this planet’s atmosphere to make it habitable for their armies. Arakssor reveals to Lord Barset that he plans to obliterate all life on this planet, but when Harman reminds him that he owes his release to them, he agrees that they may still be of some use and allows them to live…for now.

A helicopter from The Fortitude flies over the location where the Doctor’s party have stopped and the pilot radios back confirmation that they have the group in sight. Unfortunately the weather’s too bad for them to land, but they prepare to come in as low as they can and drop a ladder down. Tragically, this means they’re going to have to leave the unconscious Professor McIntyre for now and return once the weather has improved. The Doctor realises there’s nothing they can do for him and Genevieve is forced to agree. The helicopter begins to descend…

Barset and Harman watch as the Ice Warriors wheel out the enormous sonic cannon. They also notice that with most of the Warriors busy, the permanent watch over them seems to have been loosened. Barset has a hunch that with the distress signal switched off, they’ll be able to contact The Fortitude to get help. They race out of the cavern.

The helicopter comes in to land aboard The Fortitude. The Doctor believes his mind is beginning to warm up like an old TV set - and that thought suddenly causes him great concern. He suddenly realises that they’re in more trouble than he originally thought and, almost in a panic, he turns and runs back to where the helicopter landed. As the pilot prepares to arrange for a re-fuelling, the Doctor wrenches open the helicopter door and physically manhandles him out on the deck. Ignoring the man’s angry protests, the Doctor settles into the pilot’s seat and quickly familiarises himself with the controls. He’s sure he must have flown one before, but he can’t quite remember… As the rotor blades start to turn, the side door opens and Genevieve climbs aboard and asks where they’re going. He thinks she must be crazy for coming with him, but he doesn’t have time to argue. He tells her to hold on and then the helicopter rises back into the sky.

Barset and Harman emerge onto the snowy landscape and make sure there are no Ice Warriors around. Harman is worried about their friends, who he believes are still lost out there in the wasteland, and he plans to contact The Fortitude to arrange for a rescue party to be sent out, but Barset thinks they should be the priority as they’re the ones with a bunch of homicidal aliens breathing down their necks. They spot some Ice Warriors ahead of them and prepare to go back another way, but then another group appears behind them. Before they can act, the creatures lift their arms and fire their sonic weapons straight at them. The two men scream and fall to the ground…

The helicopter manoeuvres its way through the blizzard and Genevieve protests to the Doctor that they shouldn’t really be flying in these conditions. He reminds her that she didn’t have to come along if she didn’t want to, but she says she thought he might need some help - even though she doesn’t know what he intends to do. He tells her he plans to finish something he started millions of years ago. He remembered that the radio signal was a distress call, warning of Arakssor’s escape, and he realised it would be Arakssor’s first priority to shut it down.

Ssrongar reports to Arakssor and tells him he’s destroyed the two humans who were trying to escape. The sonic cannon is now in position, but its power reserve is almost depleted. Fortunately for Arakssor, the prison’s own reactor is now attaining full function, so he orders it to be connected to the sonic cannon. Suddenly they detect the approach of a flying craft - which means the humans must have lied to them when they said they only had access to a sailing ship. As the helicopter comes into view, they realise it is a relatively small vessel, so Arakssor orders Ssrongar to activate the sonic cannon to destroy it.

Ben receives a distress call from Genevieve, although it’s hard for him to make out exactly what she’s saying. He urges her to turn back, but then the radio goes completely silent. Outside the ice cave, the sonic cannon starts to power down as the reserves are exhausted. Ssrongar reports to Arakssor and tells him the flying craft was destroyed, then he brings the cannon back into the cavern and connect it to the prison reactor. Arakssor will then begin calculating how to modify the sonic beam for their purposes. Soon they will make this planet theirs!

Barset approaches the wreckage of the helicopter and cautiously calls out to any survivors. The Doctor and Genevieve emerge, a little battered and bruised but otherwise unhurt. The Doctor explains how they were shot down by the sonic cannon, but he also notices that Barset himself doesn’t look too well. He tells them he was caught by something similar, but smaller, and it hurts like hell. The Doctor says sonic vibrations are targeted at human cells and it’s not pleasant at all. Barset reveals that Harman is dead and the Ice Warriors obviously think they’ve killed him too. The Doctor admits that he made the landing look a lot bumpier than it needed to be, so hopefully the aliens think all three of them are dead and therefore they won’t be expecting them to sneak back to the base. He asks Barset if he knows what the Martians are planning to do and he tells them they’re going to do something to the atmosphere.

Ssrongar connects one end of a cable to the sonic cannon and passes the other end to another Ice Warrior, telling him to take it down to the control centre. Not far away, the Doctor, Genevieve and Barset are watching from behind cover. The Doctor can see that the cannon’s power is virtually exhausted which would explain why the helicopter wasn’t completely destroyed. If the Warriors need to recharge it, it means they still have time to save the world. They carefully sneak passed Ssrongar and head towards the main cavern.

Arakssor desperately tries to get in touch with his fellow Ice Warriors back on Mars, but there’s no response to his transmissions. He conducts a planetary scan and it slowly dawns on him that there is no life on his home planet. He realises the time of exodus has passed and immediately starts to come up with a new plan. There will be other armies to command and a new empire to build. And then he will be avenged!

In the laboratory, Genevieve collects some pain killers from the sickbay for Barset who demands a bit more compassion from the others. The Doctor’s memories continue to come back and he now recalls that he’s several centuries old and that the police box is actually his ship. Barset reminds them that the jamming signal has been switched off, so they can just call up The Fortitude and get help. When Barset guesses the signal was originally sent by Geldar, the Doctor is amazed that he knows the old Martian. Sadly, Barset tells him Arakssor had him thawed out and then murdered him in cold blood. In anger, the Doctor argues with Barset again for his questionable morals in coming on this expedition and Genevieve confirms that he just wanted to get his hands on the technology. If he intended it to be for the benefit of mankind, as he claims, then why did he keep everything so secret? Barset claims he was trying to make sure the technology united the world and would benefit ordinary people instead of being split into a million different franchises that were tied up with marketing and branding. He wanted to serve humanity without petty executives getting in the way. The Doctor says that no matter how he dresses it up, he was only interested in control and power. In some ways, he reminds the Doctor of Arakssor, because people he brought here have died. Genevieve breaks the news to Barset that Professor McIntyre is dead. He’s sorry, but that doesn’t help. The Doctor needs more information about what the Ice Warriors plan to do to the atmosphere.

Genevieve doesn’t understand how sonic vibrations from the cannon could change the molecular structure of the Earth’s greenhouse gases. The Doctor explains that Arakssor is actually something of a genius despite his brutish nature. He’s going to evaporate the heat out of the Earth’s atmosphere until the temperature eventually reaches minus 32 degrees Celsius and the human race will be frozen out of existence. The Doctor says they need to get back to the TARDIS and he tells Genevieve and Barset to pick up the batteries. As long as the Ice Warriors think they’re all dead, they should have ample opportunity to cause mischief…

Arakssor studies the equipment in the cavern and is delighted to see that the planet’s gases are starting to change. He boosts the power coming direct from the reactor to the cannon, keen to make the environment colder as quickly as possible. On the surface, the Doctor can also see that the cannon is starting to have an effect on the atmosphere. Genevieve and Barset take cover as huge chunks of ice begin dropping from the ceiling. At first they think the cannon has started an avalanche, but they’re actually giant frozen hailstones. The Doctor tries to lead them to safety, but Barset is hit by a huge lump of ice and falls to the ground, unconscious. The Doctor and Genevieve help him up and carry him into the tunnels, but they have no choice but to leave him in one of the smaller chambers and come back for him later. Later, they arrive in the main chamber. The Doctor isn’t surprised to see the Ice Warriors have ripped out the heat emitter power lines in order to prevent them being used as weapons. He decides to take one of the emitters inside the TARDIS, but then he suddenly realises he doesn’t have the key! It must have been in his pocket when he was frozen, but he’s not wearing his original clothes any more. Genevieve remembers the key that was sticking out of the police box when it was first uncovered and she’d put it in her pocket then forgotten all about it. She’s a little sceptical that an advanced spaceship can be opened with such a small key, so he invites her to try. They both enter the TARDIS and the Doctor gets straight to work while Genevieve stares at the inside of the ship in amazement.

Ssrongar learns that one of the sentries has found the wreckage of the flying craft and discovered there were no bodies inside. Arakssor has also received a report of movement inside the main chamber, so Ssrongar is sent to investigate immediately.

The Doctor programmes the TARDIS to scan for any spaceship within transmission range then attaches the heat emitter to a battery. Genevieve realises the Doctor has now recovered all his memories and she attributes it to the sound he’s been hearing - a recognition code unlocking the secrets of his mind. The Doctor thinks she’s a genius and rushes over to kiss her. He says the wave form of the distress signal will have certain characteristics in it, bits of sound that are common to all Martian technology. That’s the key to finding an Ice Warrior’s spaceship. The sound of the signal is still in his mind, so he links himself to the telepathic circuits of the TARDIS.

The Commander of The Fortitude asks Ben if he’s had any luck getting through to the naval patrol in the area, but the storm still seems to be messing all the transmissions up. Unfortunately the weather’s too bad to take the ship out to sea so they have no choice but to sit tight. There are hailstones the size of footballs and the clouds look like the end of the world is coming. Ben just hopes Genevieve is alright wherever she is.

The Doctor opens up the scanner and shows Genevieve the Milky Way. He points to a tiny little blinking light that means there’s an Ice Warrior spaceship within reasonable range. They have hyperdrive, so being on the other side of the galaxy won’t pose too much of a problem for them. He makes a note of the co-ordinates then prepares to reactivate and boost the distress signal, but in order to do that he’s going to have to use power from the reactor that Arakssor is currently using for his sonic cannon. He adjusts the scanner to see what’s outside the TARDIS - and they see an Ice Warrior waiting. The Doctor decides it’s time to take the initiative. He asks Genevieve to pass him the heat emitter.

The Doctor emerges from the TARDIS and greets the Ice Warrior before switching on the heat emitter. The creature tries to fire its sonic weapon, but in his distressed state the shot goes wide. Genevieve emerges and asks if it’s dead, but the Doctor thinks not. He asks her to collect all the other batteries and wire them up to the heat emitters in the chamber, then switch on as quickly as she can. He strides off to confront Arakssor, who is pleased to see that the damage to the atmosphere will soon be irreversible. Once the human scientists realise what’s happening, he plans to issue his ultimatum. The Doctor arrives and warns Arakssor that a Martian warship is on its way here and when the warrior doesn’t believe him, he offers to take him back to the TARDIS to prove it. Arakssor is confident he can destroy any incoming spaceship with the sonic cannon and surprisingly the Doctor appears to support this option, pointing out that if he re-directs the cannon now, there’s still time to save the human race. Arakssor says it would only be a brief respite, but the Doctor insists that mercy is never pointless. Arakssor considers for a moment, but then decides he doesn’t trust the Doctor or his craft, so he will instead go to the communications chamber where he can check the inward bound spaceship for himself.

In the main chamber, Genevieve finishes connecting the emitters and prepares to turn the heat up. Fortunately it seems to be working, but just then an angry Lord Barset races in, demanding to know why he was left for dead! Genevieve says he’s caused enough trouble already and orders him to sit down and be quiet. She tells him his problem is that he thinks money is the answer to everything, but he argues that it’s a fact of life and he’s just a victim of it. He explains that he wanted to free mankind from all that by giving them new technologies and new ways of living, but Genevieve knows he just wanted to be remembered as a great benefactor and the saviour of the human race. Barset believes they’re wasting time and decides to take direct action. He finds one of the guns left behind after his men were killed and goes off to hunt for the enemy. Genevieve races after him…

The Doctor advises Arakssor that he’s going to have to siphon off some of the reactor power, but the Warrior refuses to be lectured and insists that he already knows what he’s doing. When Arakssor operates the control, panel the Doctor notes its location with great care and observes how the power can be re-assigned to different tasks, but Arakssor orders him away from the equipment. He demands to be given the co-ordinates of the approaching warship and the Doctor is proud to say he can remember every digit. Arakssor is starting to suffer from the rising temperature, but he’s still stable enough to realise that the co-ordinates place the ship at too far a distance to have picked up the distress signal. The Doctor knew this all along - and had tricked Arakssor into re-assigning power to boost the signal. He reaches to switch it on, but Arakssor grabs the Doctor and starts to choke him. Eventually the heat becomes too much and the warrior collapses to the floor. Free at last, the Doctor is able to turn on the signal to attract the Martian ship in deep space.

When the emitters finally break down, Genevieve realises there won’t be any more heat. Armed with discarded weapons, she and Barset make their way to the communications chamber where they see a recovering Arakssor choking the life out of the Doctor again. Barset opens fire and orders the Ice Warrior to release his prisoner, then he encourages the Doctor to complete whatever it was he was doing. Delighted, the Doctor forces one last burst of power out of the reactor, ensuring that the distress signal reaches its intended target. He advises Barset to keep a close eye on Arakssor - it’s starting to get very cold again so the creature will be regaining its strength rapidly. Unfortunately the distraction is enough for Arakssor to get the upper hand and he blasts Barset dead with his sonic weapon. The Doctor angrily reminds Arakssor that he owes his survival to Barset, but the warrior dismisses him as a fool. He has also grown tired of the Doctor’s continual existence and is about to kill him too when he’s interrupted by a message coming through on the communicator. It’s from the Martian warship which is rapidly approaching them in space in response to the distress call. Before Arakssor can stop him, the Doctor leaps forward and announces that Arakssor has escaped. The Ice Warriors in space verify the distress code and confirm the Doctor’s story. They demand to know where Geldar is and Arakssor tells them he executed him as a traitor. He asks the warship commander to state which side he’s on - the side of power and glory, or the side of those who tried to imprison him? The commander reminds him that his sentence was life imprisonment and the penalty for escape is death. He intends to carry that sentence out immediately…

The entire chamber starts to shake as the warship begins bombarding them from space. The Doctor urges the commander to stop, but the affairs of this primitive planet are of no concern to him. Arakssor mocks the Doctor and points out that his sentence will be death too - but he intends that the Doctor will die first, and raises his sonic weapon. Without a moment’s hesitation, Genevieve emerges from cover and shoots down Arakssor in a hail of machine-gun fire. The whole place is starting to collapse around them, so the Doctor and Genevieve head for the TARDIS as fast as they can. Behind them, the mortally wounded Arakssor drags himself to his feet and hurries after them. He still believes his ideals will live on after his death because it’s in his race’s blood to conquer. One day his people will rise again and another leader will take his place. Suddenly the walls of the corridor cave in and Arakssor is once again enveloped in a tidal wave of freezing icy water.