On January 15th 2197, the fighter-carrier Valiant crosses Pluto's orbital path on schedule. Executive Officer Moore reports there have been no enemy sightings, but their advance scans indicate there was hostile raider activity in the area only a few weeks earlier so they maintain a condition of high battle alert. The crew must be ready for the fight when it comes, so standard defence drills are set up and all Damocles pilots are instructed to remain on standby status.

Down in the storage hold, one of the pilots, Armstrong, is surprised to hear the ringing of a large bell, apparently coming out of nowhere. He assumes it’s his colleague O’Keefe messing about, but the ringing becomes intense - and then suddenly he goes into a strange trance. He returns to the mess to find out if any of the others heard the noise, but all he gets in response is mocking from the other crewmen. Armstrong tells them he heard a bell, but before he can elaborate further there is a proximity alert and the pilots are ordered to scramble. They all rush out, including the dazed and confused Armstrong, and begin following a carefully planned and rehearsed procedure.

EXO Moore reports to the commanding officer, Captain Tanya Oswin, that the Damocles squadron has been scrambled. Although it’s only a drill, if they don’t get space borne within four minutes, there will be serious trouble. They monitor the crew’s reaction and are surprised to find there’s been no response yet from Armstrong, as he’s normally the first off the mark. But this time, all the other pilots are ready for action with the sole exception of Armstrong. Captain Oswin orders the squadron to launch without him, but after she receives a report that Armstrong has stalled his ship, she recalls the entire fleet. He’s their finest pilot, yet he’s just jeopardised the operational efficiency of Earth’s frontline defences, upon which all their lives depend. She summons him to her office immediately.

Inside the TARDIS, the Doctor is defending his behaviour to Evelyn after she accused him of panicking. He concedes that perhaps he was a little worried for a short time, but she points out that it’s been half an hour and he’s let his tea go cold. He’s still distracted by the instruments so she asks what’s bothering him and he admits that something he saw scared him and he’s not sure why. All he knows is they were about to materialise when at the last minute he discovered they’d slipped two or three centuries into Evelyn’s future. There was something very wrong about the readings - he knows Earth well enough to treat it like an old friend, but this time, just for a second, he got the feeling that he’d stumbled in on complete strangers. Something was so terribly wrong that he can’t even describe it. He panicked for a moment, flipped everything into reverse and they shot backwards in time and straight out into deep space. They’re still floating gently back through time and heading for Evelyn’s century, yet for some reason that he doesn’t understand, he’s still afraid. They hear a strange bell ringing and the Doctor tries to find a match for it in the TARDIS databank. It turns out to be something from Earth around 1950, which is odd as they’re currently not far from Pluto in the year 2197. Suddenly the sound stops and the Doctor discovers there is no longer any record of it in the ship’s computer. It’s as if the sound never existed, which they know is nonsense. He decides to find some answers…

Captain Oswin questions Armstrong, but his answers aren’t making any sense. He tells her about the bell, but she points out that no one else heard it. He becomes distressed as if the sound had awoken some long lost memory that fills him with fear. He breaks down in tears, so she has no choice but to suspend him until he can undergo a medical examination.

The Doctor and Evelyn have emerged from the TARDIS into what looks very much like the inside of an aircraft carrier. He tells her it’s the same principle - a large vessel supporting a squadron of fighter aircraft - but instead of a runway they’re looking at a launch pad from which the Damocles vessels shoot straight out into space. They’re the deadliest fighter craft of their age, the envy of their enemies. This is obviously a military vessel, so Evelyn is worried about the reaction the crew will have to two strangers wandering around. He assures her they’re not going to stay long as he just needs to take a few readings. Just then, they are confronted by an armed officer who orders the Doctor to drop his tracker. He does so, and the device smashes on the floor, just as he predicted it would.

EXO Moore reports to Captain Oswin that crewman O’Keefe has discovered two strangers. The prisoners are escorted onto the bridge and introduce themselves. Oswin makes it clear that she’s likely to loose her temper very quickly and have them shot if they don’t provide some answers. Her orders are to protect Earth’s solar system from alien raiding parties which have caused unacceptable levels of damage and loss of life over the last decade. She runs a squadron of highly trained military personnel ready to engage the enemy and she hasn’t got the time or the patience to listen to them prattling on about bells. The Doctor interprets this as permission to leave, but Moore wants to know exactly where he’s planning to go. Oswin pursues this line of questioning - did they stow away before lift-off or have they only just arrived? The crew detected no other spaceships in the area recently, so the Captain orders the Doctor and Evelyn to be frozen so they can be interrogated properly when they get back to Earth. As they’re being escorted off the bridge, the Doctor asks Oswin whether the sound of a bell means anything to her, and it’s clear from her reaction that it does. Moore explains that one of their pilots claims to have heard it, but there’s something wrong with him. Before they can discuss it further, there is another operations alert and the pilots are scrambled to deal with two confirmed raider contacts.

The Doctor and Evelyn are bundled rather brutally into the ship‘s brig. He’s confident they can escape while the crew are preoccupied, but Evelyn is worried that the TARDIS has probably been thrown into space by now. He decides to ask the pilot Armstrong some questions, and he deduces from their earlier conversation with the Captain that he’s likely to be found in the sickbay. First, they must escape from their cell and fortunately the Doctor recalls that Earth military security locks in the late 22nd century are rather susceptible to high frequency vibrations. He still hasn’t got round to building a new sonic screwdriver, so instead he scrapes his fingernails down the metal wall until he finds the correct pitch. Evelyn kicks the door open and the two of them set off to explore.

As the Damocles pilots launch from the ship, they receive orders to plot an intercept course with the raiders who were last seen near the Jupiter moon ore station. Pilot O’Keefe reports that they have the enemy under surveillance and their weapons are armed and ready to deploy. Their targets suddenly break for cover behind the moon of Io and the pilots go in pursuit, keeping a watch out for deadly ion-trails. They’re likely to lose visual contact very soon and will depend on accurate tracking data from EXO Moore. Unknown to anyone, however, Moore is going into a trance after hearing the sound of a bell tolling inside his head.

As the Doctor and Evelyn continue their search, he tells her about an Andosian privateer he once met called Dr Leopard. He was eight feet tall, had rippling mauve muscles and three heads. Apparently the Andosian leaders always chose melodramatic names, but Evelyn thinks is sounds more camp than anything. As they follow some arrows marked with red crosses, the Doctor tells Evelyn more about the thing that scared him. He asks if she’s ever experienced dreams where you go back to your childhood home only to find that everything’s changed. You know it should be familiar, but not one thing is as you remember it. Evelyn has never had a dream like that, so perhaps it’s unique to Time Lords. A nearby door opens and they step back to allow a group of soldiers pass by. Obviously the battle alert is still on.

The pilots report that visual contact has been lost and Oswin demands to know what happened to the tracking that Moore is supposed to have been providing. He’s still hearing the bell in his head and is pleading for it to stop. At that moment, the pilots see the enemy ships immediately in front of them and all contact is lost following what sounds like a space collision. Oswin turns to Moore in horror. The alien raiders are now out of range and there’s no signal from any of the Damocles fighters. She’s furious with her Executive Officer - they’ve lost the entire squadron and it’s all his fault. He seems barely able to understand what she’s saying and can only hear the sound of the bell…

The Doctor and Evelyn arrive at the sickbay but before they can decide on the best approach to take, the door opens and the dishevelled figure of Armstrong emerges. The Doctor mentions the bell to him and Armstrong wonders why no one else can hear it. He walks off in a trace, muttering incoherently to himself, so they follow him. When they arrive back at the storage bay they can’t believe their luck - he’s taken them straight back to the TARDIS. The Doctor asks her to keep the pilot occupied while he goes inside to check some readings. Evelyn notices that Armstrong seems particularly interested in a large metal door which he claims leads to nowhere! Inside the TARDIS, the Doctor is watching on the scanner but he doesn’t remember seeing the door before. When he hears the bell, he checks his instruments…but what he sees can’t possibly be right!

The bridge crew has still been unable to pick up any transponder codes from the missing squadron. Oswin tries to find out what happened to Moore, but he’s broken down and is crying at his post. He insists he can hear the bell and she calls sickbay. The embarrassed medical staff report that Armstrong seems to have slipped out somehow. The Captain contacts the Master-at-Arms and tells him to find the missing crewman. Suddenly the Damocles transponder codes are detected again and Oswin asks to be patched through to O’Keefe. He explains that they got caught in an ion-trail and lost one of the pilots. His voice keeps cutting out due to on-board systems failures. He asks why the Valiant didn’t send through any tracking data, but the Captain is reluctant to discuss what happened and she recalls the pilots back to the ship. The Master-at-Arms reports back to Oswin that the Doctor and Evelyn have escaped from the brig. There wasn’t a guard on the door because all personnel were called to secure stations. There’s still no sign of Armstrong, but they’ve now located their prisoners in the storage bay. Moore seems to be feeling better, so she tells him to join her and the team down in the storage bay…

Evelyn tells the Doctor what Armstrong said just before he went through the door. Although there was nothing on the other side, they definitely heard the bell tolling. He goes to the wall and tries to listen, and at first there’s nothing. Then he hears something - incredibly, it’s a steam train! He realises that Evelyn can’t hear it, even when the train rings it’s signal bell to indicate it’s arriving at a station. Then he hears the ticket inspector speaking and Evelyn starts to wonder whether he’s picking up telepathy rather than an actual sound. There are definitely people talking and he’s sure it sounds familiar - but why isn’t he being drawn to the door like Armstrong was, and why isn’t it opening? The Doctor realises the sequence of sounds is repeating itself. Evelyn theorises that the sounds are coming from the past, but how, and why?

Inside the TARDIS, the Doctor manages to isolate the sound of the train and at last Evelyn can hear it too. Fortunately the Doctor was a train spotter for a time and although he’s a bit rusty now, he narrows the sound down with a little help from the databank. It’s a train that was withdrawn from the Northern & Western line in 1953. The sound came from 7th September 1952 and they narrow it down to the Stapely Moor Riverside line and a Turret-class locomotive called the Ivy Lee. Before they leave, the Doctor wants to get a sample from the door as it’s obviously not part of the actual ship even though it looks exactly like all the other doors. Unfortunately they get caught and Oswin points out that because she hasn’t had time to enter them in her log, they officially don’t exist. If they’re not careful, she could make that permanent. The Doctor and Evelyn tell them what happened to Armstrong and Moore reacts when they mention the bell. He demands to know what was behind the door, and Oswin threatens to shoot the Doctor on the spot when he starts to hear the train as well. Suddenly Moore crosses to the door and opens it. The others try to stop him, but it’s too late and he disappears into nowhere. The crew manage to slam the door shut behind him and Oswin decides it’s time she finally got the truth from their visitors. The Doctor and Evelyn swear they don’t know anything, but Oswin posts guards outside the storage hold and has her prisoners escorted to her office.

The Captain orders the ship to go to maximum security with full security protocols observed at all times. The Damocles fighters are cleared to land, but unusually the crew are ordered to remain in their ships on battle readiness. The Valiant is on security lockdown because of an intruder alert - they may be under attack!

Captain Oswin asks the Master-at-Arms to leave her alone with the Doctor and Evelyn. She asks them whether they’re responsible for the door in the storage hold, even though she already knows the answer. Unfortunately the Doctor doesn’t have any facts and he doesn’t even know whether the door is alien, but she’s lost two crewmen already and she’s becoming desperate. Evelyn decides it’s time to tell the truth - she says they’re travellers in time and space and the blue crate in the hold is their ship. She explains why they came to the Valiant and points out that they first heard the bell before they arrived here. Just then an alarm sounds indicating problems at the storage bay. She contacts the Master-at-Arms and learns that the door has opened again and two guards have already been lost. The problem is getting worse and the Doctor is certain this is going to continue happening. Oswin orders the hold to be sealed off permanently and sends out the Damocles fighters to set up a defensive zone around the ship. The Doctor asks for his ship to be removed, but when she refuses he decides to adopt Evelyn’s approach. He tells Oswin he is a Time Lord and came here out of a concern for the human race. He believes he may be the solution to their problem, but it depends on whether he can have access to his ship. His plan is to travel back to 1952 to the railway line where the Ivy Lee is based. Their only lead is the origin of the sound that people seem to hear before they are sucked to their deaths. She agrees to a compromise - she will remove the TARDIS from the hold, but it would be a dereliction of her duty to allow him access to it.

Oswin prepares a Priority 1 coded message to summon help, but before she can send it the door in the storage hold opens again. The Master-at-Arms reports that he doesn’t have enough men left to stop the number of people trying to get through to it. She orders him to disable the crew by shooting them if necessary, but the Doctor doesn’t think anything can stop them. There’s some higher power at work here, something beyond all the physical laws of the Universe. The door shuts again, by which time they’ve lost another ten people. She orders them to weld the hold shut before it happens again. She sends the report to Earth, explaining that an unknown alien force has breached the ship’s hull and is abducting crew members. All efforts to identify the cause have failed and the frequency and severity of the attacks is increasing. Intruders have been held in cryogenic suspension for questioning and their craft held for analysis. She requests a full military taskforce to be sent to their aid as soon as possible.

Oswin tells the Doctor the taskforce won’t arrive for another two months and he assures her that will be far too late. She has no way of verifying anything the Doctor and Evelyn have said, but for what it’s worth she doesn’t think they’re responsible for what’s happening. She claims she doesn’t have the authority to act on her gut feeling, but the Doctor points out that there simply isn’t time to follow the normal chain of command. They have no idea who will hear the bell next - it could be her, it could even be the entire crew! He doesn’t know why the bell hasn’t had any effect on him. Evelyn suggests freezing everyone on board, and Oswin agrees that this may yet be an option. The alarm sounds again to indicate the door is opening. Oswin orders a passing crewman to escort the prisoners to the sickbay for freezing.

The Damocles fighters have successfully set up the exclusion zone around the Valiant and await their next orders. There’s no sign of any alien incursion or of any hull breach near the location of the storage bay. Suddenly pilot leader O’Keefe hears a bell ringing inside his head…

The crewman escorting the Doctor and Evelyn also hears the bell and he leaves them unguarded as he heads straight for the storage bay. The effect is obviously spreading, and the Doctor realises if they stay here on the ship the best they can hope to do is patch up a crumbling dam.

The Doctor refuses to listen to Oswin’s threats and drags Evelyn towards the TARDIS. The Master-at-Arms reports there are 30 crewmembers heading for the hold, and even though they can no longer get through to the door, the Doctor warns they will probably tear themselves apart trying. The Doctor insists they’re dealing with something so alien to the nature of time and space that even he was repelled, like an animal retreating from fire. When he first saw it, it was as though something primal had been trigged within him. As he struggles to hold back Evelyn, he finally realises that he has to face that fear and defeat it. Oswin accepts that it’s pointless trying to stop him, so she helps him get his friend over to the TARDIS. She asks only one thing - will he promise to come back..?

Inside the TARDIS, Evelyn bangs on the door, begging to be let back out again. Eventually she’s restored to normal, but is still in a state of shock and can only remember hearing the words ‘Time’s End‘ over and over again. She sits down while he sets the course for Stapely Moor on 7th September 1952. The Doctor asks Evelyn where she heard about Time’s End and she vaguely recalls seeing faces screaming in terror. He assures her that what she saw is nearly 250 years in the future and they’re safe now. The TARDIS lands and they find they’re aboard a moving train. They decide to explore, but before they leave Evelyn tells the Doctor that the words she heard were coming from a gigantic mouth that was about to swallow the screaming faces! He wonders what exactly is waiting for them outside the ship…

In a first-class compartment aboard the Ivy Lee, Trevor Ridgely is struggling with the crossword. He reads out one of the clues to his colleague Palmer, even though he knows the man won’t answer. They’ve been on assignment together for months, and Palmer has never been one for trivial conversation. Ridgely asks whether it’s just him that Palmer won’t talk to, or is he like that to all his charges? He decides to construct a mathematical formula in his head to predict Palmer’s responses to certain stimuli. Just then, Evelyn walks through the carriage and Ridgely notices Palmer’s eyes flicker for a moment to see who it was. He teases the silent man, suggesting that the woman might be a Russian spy, or perhaps Chinese. He gets no response and wonders what it will take to really annoy his colleague.

The Doctor and Evelyn meet up, having each wandered down both ends of the train to see who else is aboard. She’s amused by his disguise as a ticket inspector, especially as the clothes are a bit short for him. There doesn’t appear to be a guard on board, so they have the night train all to themselves - and the two men that Evelyn saw. At that moment, one of the men enters their carriage so the Doctor asks to see his ticket. As Palmer reluctantly hands over his ticket, he demands to know what they’re doing on the train as it’s not usual to have a guard, let alone other passengers. Evelyn asks the ‘guard’ to protect her from the brusque questioning she’s receiving, but the Doctor’s blustering response doesn’t help. She claims to have joined the train at Stapely Moor, until Palmer points out it doesn’t stop at that station. The Doctor assures him it did tonight and asks him whether he heard the signal bell. Palmer seems unsure, but leaves anyway. The Doctor tells Evelyn that he heard the train stopping through the door on the Valiant, so perhaps it’s significant that this was the only night that the Ivy Lee stopped there. He guesses that Palmer is a regular traveller on this route and is so stuck in his routine that he wasn’t concentrating. What’s interesting is that the documents he produced weren’t rail tickets at all, but War Office travel warrants, signed by the Secretary of State himself. The sole passengers on this train are obviously engaged in a mission of national importance. They now have two ‘suspects’ and the Doctor decides it’s time Evelyn questioned them! He suggests she adopt the guise of a lonely old lady in need of some company…

When Palmer returns to the compartment, Ridgely tries to find out who the mystery woman was, but gets no response. He dismisses his colleague as an annoying ape. Just then, Evelyn enters and asks if they mind whether she joins them. Ridgely welcomes her and apologises for his non-talkative companion, but Evelyn points out that he was talkative enough earlier when he cross-questioned her in the corridor. They introduce themselves and she ‘confirms’ that she’s heading to the same destination as they are, which surprises him, even though no one at the base knows what any of the other people are working on. Palmer demands to see her ticket, and when she claims to have given it to the train guard, he leaves the compartment to check. Evelyn tries some gentle coaxing and learns that their destination is known as Hill Langton and all the ‘brains’ from the country are working there on top secret projects for the War Office. She’s shocked, however, when he jokingly refers to their lords and masters as plotting the end of the world!

Palmer finds the Doctor and demands he shows him the “old bag’s” travel warrant and the Doctor flusters through a weak explanation about leaving it in the guard’s van. Palmer insists on accompanying him while he goes to get it..

Evelyn notices that Ridgely has drawn a doodle on his crossword that disturbs her as it looks a bit like a spaceship. He dismisses it as just an idea he’s been messing about with just to relieve his boredom. His physics lecturer at Oxford always told him he had an overactive imagination, but he can’t help himself scribbling things down without knowing it. Pleased by her interest, he shows her details of his work on rocket propulsion, but she’s more interested in hearing more about his ideas for the future. He can’t believe the destiny of mankind is just to lob ballistic missiles at each other - one day they’ll put all this behind them and strike out across the stars. Just then, Palmer returns and is outraged to find that Ridgely has been showing the strange woman classified material. The Doctor joins them, still pretending to be the train guard, and tries to calm the situation down. Ridgely assures Palmer that he hasn’t been showing her any secrets, just doodles he’s been working on for his hobby. Palmer screws up the paper and Ridgely protests as it’s his only copy. Evelyn retrieves the doodle, and Palmer is reminded that he still hasn’t seen her travel documents. Evelyn tries to leave and the Doctor arouses Palmer’s suspicions by calling her by her first name. The Doctor realises Evelyn is slipping into a trance, but before he can stop her she knocks him and Palmer to the floor and races out of the compartment. The Doctor asks Ridgely about his sketches and he confirms that they’re spaceship engine designs that he’s working on just to amuse himself. The Doctor recognises it as a Stardrive and is shocked to find the paper Evelyn took was the only copy in existence!

The Doctor manages to snatch the papers from Evelyn’s grasp. She demands he give them back so she can destroy them. She knows Ridgely will never commit his ideas to paper again and if this copy is lost today, mankind will travel no further. Evelyn starts to talk with an alien voice and the Doctor asks who it is that he’s really talking to. He now knows that he was deliberately brought here for a purpose which is why he was able to hear the sound of the train through the door on the Valiant. The voice of the ticket collector that he heard was his own voice! He tries to tempt Evelyn back on to the train, but she jumps and he has to grab her arms. Fortunately Palmer arrives and together they manage to physically drag her back aboard. Ridgely joins them and when Palmer spots the police box he concludes that the Doctor must be an undercover policeman. Using the combined might of all three of them, they manage to shove the struggling Evelyn inside the TARDIS.

The Doctor thanks Palmer and Ridgely for their help in this case and tells them their department head will receive the usual paperwork in due course. The bemused men accept his assurances. The Doctor returns Ridgely’s papers and implores him to keep them safe. They’re not important right now, but one day they will be. He tells them the military police from Hill Langton should be waiting for them when they arrive and Palmer’s suspicions are aroused again. He asks to see the Doctor’s warrant card, so he goes inside the police box to get it…

Inside the TARDIS, a shell-shocked Evelyn tells the Doctor what else she heard - the words “travel no further”. She has no recollection of going back to the TARDIS and the last thing she remembers is the drawing of a spaceship. The Doctor assures her Ridgely’s designs weren’t just idle fantasies, they actually made sense. He sets the TARDIS to return to the Valiant. He now knows that whatever is behind the door to nowhere, it tricked them into going back to 1952. It wanted mankind’s ability to travel in space to be wiped from history by forcing Evelyn to destroy the original germ of Ridgley’s idea.

Back on the Valiant in 2197, Captain Oswin receives confirmation that a military taskforce, headed by the Exeter, is approaching. Despite interference from the door in space, she manages to contact the fleet and explains their situation to the rescue team. She warns of an alien force on the starboard hull and tells them her crew is down to less than one quarter strength. At that moment, the TARDIS re-materialises and the Doctor emerges. Oswin demands to know why he wasn’t able to stop the crisis, despite his earlier promises. She accuses him of failing in his mission and now believes the problem is never going to stop until the whole human race is sucked through the door. They’ve already lost hundreds of their crew and their attempts to freeze the remaining crew members didn’t work. Fortunately the reinforcements have just arrived and when the Doctor says he doesn’t think they will do any good, she points out that the Exeter has nuclear capability. She can’t afford the luxury of indulging the Doctor’s hunches any more. As the door is currently closed, it’s safe for Evelyn to come out of the TARDIS. They explain to Oswin that someone or something is trying to stop the human race from travelling into space. Without warning, the Doctor suddenly runs back into the TARDIS and takes off, leaving Evelyn behind. Oswin believes he’s now abandoned even his own friend and she wonders why she ever trusted him.

The alarm sounds to alert them to the door opening again and Evelyn is resigned to the fact that whatever happens now, she will be forced to go through into nowhere. But just then, they see the TARDIS materialising right in front of the door, blocking off all access. The Doctor locks off the ship’s drift compensators and then opens the TARDIS door. There’s absolutely nothing on the other side - he’s looking out into nowhere. He calls out to whoever might be listening and insists that he will stop them from dragging any more human souls through the door. A huge alien voice booms instructions to him, telling him to get out of his way. The voice says it is always here and when the Doctor refuses to move, it tries to shake him over the edge.

On the Valiant, Oswin and Evelyn watch as the TARDIS starts to physically vibrate in front of the door. Believing that the alien threat is trying to shake the obstruction free, Oswin contacts the commander of the Exeter and tells them to fire everything they have at the door and blast it out of existence. Ignoring Evelyn’s protests, she sends the target co-ordinates over to the fleet.

Aboard the TARDIS, the Cloister Bell starts ringing and the Doctor hurries back to the controls. The alien voice again demands that he get out of its way, but it’s too late. The Doctor has captured the door within the TARDIS’s force field and dematerialises. Now the alien is stuck with him and will be forced to go wherever the Doctor wants to take it!

Oswin and Evelyn are amazed to see both the TARDIS and the door disappear. However, Oswin believes the threat still exists - perhaps the door has just become invisible, or perhaps the door itself has gone but the alien behind it has been set free? She orders the nuclear bombardment to continue. She tells Evelyn that the TARDIS was gone for two months and during that time she saw hundreds of her people get dragged away, including many good friends. She implores Evelyn not to argue with her any more.

The TARDIS and the door are now drifting in space. The Doctor assumes that the alien must be from a space travelling race and asks his unwelcome guest if there’s anywhere particular they’d like to go. An apparition of Trevor Ridgely appears in the control room and passes the Doctor a set of co-ordinates. The Doctor wants to see the alien’s real face, but Ridgely warns him that if he doesn’t do what he says he will rip the TARDIS apart. The Doctor agrees and the TARDIS dematerialises…and they find themselves at Time’s End. The alien says it is always here, and now he will be too.

The space fleet confirm their target and prepare to launch the nuclear weapons. Evelyn points out that at this range, the weapons will destroy the Valiant and the entire taskforce, but Oswin is aware of this and gives the order for the ships to evacuate. All surviving crewmembers are told to disembark and shuttle across to the Exeter. Evelyn refuses to join them and prefers to wait here for the Doctor to return.

The Doctor’s ears are being bombarded with a strange noise and for a moment he even considers rupturing the time core of the TARDIS if the only alternative is spending eternity listening to that. Eventually the noise dies down. The apparition of Ridgely shows the Doctor it’s real form, and although he doesn’t recognise the species, he does recall Evelyn’s description of the mouth swallowing the screaming faces. Ridgely invites the Doctor to look inside, and at first he’s afraid - but then he sees billions upon billions of creatures being crushed and pulverised. The Doctor realises he’s in some kind of space capsule and he’s witnessing an accident. He can’t identify the technology, but he does recognise the Stardrive controls that warp space to enable the ship to travel faster than light. The alien shows the Doctor his people on the screen - and he slowly starts to realise…he’s seeing an image of Earth as it was fifty billion years ago!

The crew from the military taskforce have all assembled aboard the Exeter and the commander is ready to begin the missile ignition sequence. He notices he’s reading one human lifeform still aboard the Valiant and he accuses Oswin of leaving someone behind. She knows, but orders the launch to begin anyway.

The alien tells the Doctor that the human race was not the only civilisation ever to evolve on Earth. The creatures he saw inside the alien’s mouth are the next species. The Doctor refuses to believe it - Time’s End is the theoretical point at which all cosmic laws break down, like light and time bending through a black hole, but unimaginably worse. All the physical forces in the Universe are depleted and distorted here. It’s the final moment of destruction for everything - an insane maelstrom of utter chaos caught in the moment between nowhere, no time and no space. And for those caught in that moment, without time or any physical laws to govern it, it is an eternity with all the chaotic forces of time and space at their disposal. An eternity where anything is possible, except reason.

The Doctor is truly sorry. He offers to find out what happened and try to put things right, but then he realises if he does that, the human race will never have existed. The creatures in the alien’s mouth are all species that evolved on Earth and that the aliens’ first mission to travel beyond their solar system must have ended in disaster. They found themselves experiencing severe sensory distortion caused by the effects of the time warping and when they launched, the forces released were so terrible, their entire species was ripped out of time and space. Billions of other dominant races have evolved since then, but as the Doctor doesn’t recognise a single one of them, he realises all those races have been ripped out of time as well. The human race is only the most recent, but there will be others later. Each time one of those races reached the edge of the Solar System, the aliens proclaimed they must travel no further and the entirety of a whole intelligence species and their history were sucked through their doorway and out of time and space. It’s as if they never existed, reduced to a screaming singularity of pulverised matter inside the aliens’ mouth. Anything is possible at Time’s End. The Doctor accuses them of eternal genocide, but the aliens believe it is their sole absolute right to travel the cosmos. Why should anyone else have that ability? The Doctor is shocked. That’s the reason the aliens have done all this, because they’re jealous - they believe they’ve been betrayed and overlooked.

Oswin mutters an apology to the Doctor and Evelyn - then orders the nuclear missiles to be fired. Aboard the Valiant, Evelyn watches in horror as the warheads approach…

The Doctor examines the alien spaceship and spots a mis-setting of the co-ordinates. The ones currently in place would have caused the hyperspace equivalent of a Mobius strip, which means the engines were caught up in their own time warp. They made a simple mistake in the heat of the moment that had catastrophic consequences. The aliens urge him to correct the settings, but on closer examination the Doctor can see how this mistake would have destroyed the alien ship and killed their race, but not how it could have removed them from time altogether. The alien implores him again to change the co-ordinates, but he wants to know more about their bitterness, about their unfulfilled dreams and their sense of failure. He finally realises that what led them to commit genocide billions of times over was simply their fear that their existence meant nothing. In their minds, that gave them the right to destroy every chance the Earth had of producing a successful species and condemning them all to eternal suffering. To the Doctor this is so diabolical, it’s almost beyond his comprehension.

The aliens insist they deserve a second chance, but the Doctor knows that if he saves them now, none of the other species - the human race and all its countless unknown predecessors - will ever have existed. But he can’t shake the feeling that there’s still something missing. What brought them all the way here to Time’s End? The Doctor has already seen the future of the human race and he knows they will eventually move beyond the Solar System. They will develop Stardrives, almost exactly like the ones Trevor Ridgely was working on. And that’s why the Doctor is here - to make sure the destiny of Earth is safe. He can only guess at the consequences of his actions, but he agrees to change to co-ordinates to set up a linear path that will make sense to the aliens. The aliens thank him, but it’s too early for that. The insane way that Time’s End works means they’re here at the end of time; they’re about to set off on their first mission; they’re in 2197 as well as countless other times all at the same time - they’re everywhere and nowhere. There’s no order to events and everything has been distorted beyond all shape and reason. Something that happened millennia ago could happen in the next second.

The Doctor recalls Captain Tanya Oswin had a rash plan that he’d advised against, but she’d taken a gamble on him once and had been let down badly, so she would never take that risk again. They hear a sound in the background which means that time is starting to warp as their Stardrive engages. At that moment there’s a massive influx of raw nuclear energy and the Doctor rushes to the TARDIS and dematerialises. Suddenly there is a massive explosion as the whole of time and space rip apart…

The TARDIS arrives back on the Valiant where a confused Evelyn is waiting for him. She thought for one moment that he’d left her to get blown up in a nuclear explosion. The Doctor is sad that he wasn’t able to save the aliens or any of the other races that made up the screaming faces, but they were lost forever when the nowhere place moved. He reassures her that the doorway won’t come back. Behind the door was just a blind alley for history, but it was shut off permanently when Oswin fired the missile. That action was what first made the nowhere place possible, but because he changed the co-ordinates, the trajectory of the ship was altered. At Time’s End every moment in history is happening all at once, so this time Oswin’s missiles destroyed the nowhere place, causing billions of possible timelines to evaporate. Evelyn wonders if this was the right thing to do, but he has to believe that it was. At least, he chooses to believe that it was…