Boarding the tiny shuttle that will take them to the waterfall, the Doctor and the other passengers are greeted by the stewardess, who hands out their complementary supplies for the journey. The Doctor chimes “allons-y” with the enthusiasm of departing, much to the Hostess’ disinterest. Amongst those travelling are Professor Hobbes and his assistant Dee Dee Blasco, who are conducting a scientific study of the planet. Also onboard is the Cane family, namely couple Val and Biff and their teenage son Jethro. After being greeted by the Professor the Doctor looks around and observes a rather austere looking woman sitting nearby, who resigns herself to reading a book as the other passengers take their seats.
Soon the shuttle is ready to leave, and the hostess ensures that the capsule is fully sealed and the occupants fully secured before takeoff. She reminds the passengers that the planet outside has no air so they must not open the portals, and then points out the emergency exits.
Driver Joe, speaking over an intercom from the sealed-off cabin, tells his travellers that they will be taking a slight detour due to a rock fall, but the journey will otherwise remain unchanged. He starts the engines and as they move off the Hostess introduces the onboard entertainment – a garish selection of videos, film and light projections that flood the cabin via small screens built into the ceiling, much to the passengers’ distaste.
Sensing the entertainment will not go down well, the Doctor disables it with his Sonic Screwdriver then turns to his fellow travellers and tells them they will all have to talk to one another instead – something they initially seem somewhat reserved about. However, soon they are speaking jovially, all bar Jethro – who remains sat sullenly in the corner, and the austere woman at the front, who doesn’t say anything.
As the journey progresses, the Doctor finds himself talking to Dee Dee about her work – namely the paper she wrote about the Lost Moon of Poosh, and her time as an assistant to the Professor.
After a while he befriends the woman sitting alone at the front of the capsule, who explains she is trying to overcome a recent relationship breakdown. The Doctor sympathises with the experience – citing that one of his friends parted with him by ending up in a parallel dimension.
Later on, Professor Hobbs gives a presentation about Midnight, and proudly notes that he is the first to examine the planet – which is bombarded with Extonic Sunlight (deadly radiation). He claims that Midnight, as well as it’s entire planetary system, is notable by it’s lack of history – as no life can exist on any of the planets without protection. Jethro asks if anyone has searched the planet for signs of life and the Professor explains that because no one can step outside (even the leisure dome Donna is residing in was lowered onto the surface from orbit), the study of the planet is more complicated than usual.
Suddenly the capsule hits a bout of turbulence and then grinds to a halt. A worried Hostess asks the passengers to return to their seats, but the Doctor is curious as to what has gone wrong. Bluffing his way past the Hostess with his Psychic Paper he enters the cabin, where Driver Joe and his Mechanic Claude are trying to find the source of the problem – and find that all systems are functioning normally but for some reason the capsule will not move. They send out a distress call and as they begin the hour-long wait for assistance the Doctor persuades them to open the main shield at the front of the cabin.
They do so and then marvel at the beautiful landscape that stretches out before them – a staggering formation of diamond rocks all poisoned by the sun’s radiation. After a few seconds Claude notices something moving outside, but the Doctor and Joe don’t see it. As the shields close to prevent the deadly sunlight outside from penetrating the safety glass, Claude sees it again – a shadow outside running toward the capsule.
Joe sends the Doctor back to the seating area, where the passengers are concerned about the breakdown, all apart from the rather gothic Jethro, who seems somewhat delighted at the macabre goings on. Soon all of the passengers are talking at once, worried about how they are going to return to safety. The Doctor manages to restore order (and silence) then hands over to Dee Dee, who reassures the others that the air in the capsule is filtered so will last for years – they have nothing to worry about.
A moment later there is a thumping sound, as if something were knocking on the walls outside. Again Jethro seems enthused by the strange goings on, but the others remain panicked, fearing what might be on the other side of the wall. Professor Hobbs reiterates that nothing could survive in the radiation outside, but despite his claims the knocking continues, slowly moving around the cabin until it reaches the main door.
Soon the austere woman descends into hysterics, convinced whatever is causing the noise is coming for her. As the other passengers turn to her, she backs away towards the cabin door. Suddenly there is a crash and the passengers are thrown across the capsule. Showers of sparks explode all around them and then the lights go out. Eventually the ship settles and the Doctor asks if everyone is alright, unaware that on one of the screens behind him there is a mute video of a girl calling out to him – it is Rose.
The screen fades whilst the passengers begin lighting torches, which are stored behind each of the seats. Jethro looks around and finds the austere woman is still at the front of the cabin – sat on the floor, turned away from them, clutching her head. The seats around her have been torn up from the floor. The Doctor tries to comfort her but she makes no sound. Meanwhile the Hostess tries to contact Claude and Joe, but when she opens the cabin door a piercing light greets her. The passengers scream as the Hostess closes the portal. The Doctor examines some of the circuits and discovers that the cabin has been sliced off of the rest of the capsule – Claude and Joe have been reduced to dust.
He turns to the others and promises that help is on its way, then resumes talking to the woman at the front of the cabin, whom the Hostess names as Sky Silvestry. As the Doctor talks to her Jethro realises the knocking on the wall has stopped – and wonders whether whatever was causing the noise may have gotten inside.
A few seconds later Sky turns around – her eyes wide and face almost expressionless. She looks around and the Doctor talks to her, trying to reassure her that everything will be all right. However, he realises something is wrong when she begins repeating his every word. He asks her to stop but she continues – and as each of the other passengers begins talking she mimics them as well. The Doctor begins testing her and recites the square root of pie. Sky responds by reciting it as well, much to everyone else’s astonishment. Again the cabin descends into worried chatter, with Sky still copying everyone’s words.
Suddenly the lights come on and the Hostess assures the others that help will arrive soon. The Professor claims that Sky must be in a state of self-induced hysteria and should be left alone. However, both the Doctor and Jethro discover it is something far more disturbing. As the passengers talk Sky no longer repeats their words back to them – now she is talking along with them, mimicking their words as they speak them.
The Doctor confronts Sky, who is still crouched at the front of the capsule, and continues to test her newfound ability – but it proves to be infallible. He ponders what might happen next – first she repeated them, now she talks in synch with them, what next? Both Jethro and the Doctor have realised the woman before them is no longer Sky Silvestry.
The Doctor motions everyone except Sky to the back of the capsule, and assures them that they will be safe. Val claims she is still unnerved by Sky, who now sits at the front staring over at them. Jethro recalls the knocking on the wall and notes that the banging followed her along the capsule as she backed away, and stopped when it found her. Again the Professor claims that nothing could live outside, but the Doctor is sceptical, fearing that some consciousness may have taken over Sky. He claims they must try to save her but for now it is best to stay away from her – if the second step of the transformation is synchronising with people, the next stage may well be becoming them.
Out of the blue, the Hostess suggests they throw Sky out of the capsule – a suggestion that horrifies the Doctor. He claims they will not throw her out but Dee Dee begins to theorise the possibility of such an act – claiming that when the cabin door opened earlier nobody was sucked out into the planet outside because of a wall of pressure that collapses after six seconds – long enough to throw someone outside without sacrificing themselves.
The Doctor turns on the group and tells them that the creature inside sky could be a new life form, and they are not showing it the welcoming side of humanity. He claims that their actions now will define them as people, and asks if any of them could really be willing to kill someone. After a moment or two of hesitation the Hostess, Biff, Val and Dee Dee all claim that they would, and will, throw her outside to make sure that they remain safe. Again the Doctor refuses to let them commit murder but they insist they will go past him in order to throw Sky outside.
Soon they begin turning on him, even the Professor and Jethro begin admitting doubts as to the Doctor’s credentials and intentions, noting his glee at discovering the monster inside Sky. He admits he is fascinated by the new life form he has encountered but insists he means well. However the others now begin wondering what it was he said to Sky when he sat with her at the start of the trip, and what he did to the wiring when he opened up the control panel. In an outburst the Doctor claims he knows what he is doing because he is clever, a claim that enrages the group even more – now they suggest that he too should be thrown outside along with Sky.
Again the Time Lord tries to reassure his fellow travellers but they continue to turn on him, this time demanding to know his name. He claims he is called John Smith, but they all disbelieve the pseudonym. After more wrangling the passengers are surprised to discover that Sky, who is still at the front of the capsule, has ceased from talking alongside them. The Doctor speaks with her again and it becomes clear that now it is only he she is mimicking, which fuels the other passengers’ belief that he is working alongside Sky.
The Doctor asks Sky why she has latched onto his voice and what she needs it for, but he gets no reply. He realises that the creature within Sky needs him for something and he tries to reason with her – telling her that whatever she needs, be it a voice or a body, she does not have to steal it. As he tries to make a deal with her to keep everyone, including himself, safe, it becomes apparent he may be too late – now Sky is speaking first, and he is repeating.
The passengers note that the creature must have passed into the Doctor and let Sky go, and indeed she now seems to be returning to independent thought, with the Doctor repeating her words. However, Dee Dee claims this is not what has happened, but her words go unheeded.
Sky asks the Professor to get her away from the Doctor and he obliges. She gets to her feet and walks away with the other passengers, leaving the crouched Doctor alone. As she talks about being free again he repeats her words. However, unlike Sky when she was in a similar state, his voice retains some form of emotion, as if struggling to overcome the force mounting inside. His eyes are wide with fear rather than menace, and his body shivers.
Once more Dee Dee passes doubt on the idea of Sky being released from the grasp of the creature but the others all agree that she is now safe and the Doctor is contaminated. Sky tells them that the creature inside the Doctor’s head was waiting in the dark and the cold for a chance to take freedom. It is the creature that killed Joe and Claude, and now it wants to destroy the rest of the passengers.
Dee Dee claims the creature is not inside the Doctor and despite the protests of the other passengers, the Hostess insists that she be allowed to speak. She explains that, just as the Doctor said, the creature would go from repeating to synchronising to something else, and it is this next stage it currently resides at. Instead of passing from one body to another is has latched onto the Doctor and stolen his voice – it is draining him.
Again she is ignored and Sky continues to turn the others on the Doctor, claiming that he is trying to get inside their heads. Blinded by fear and lies Val, Biff and the Professor begin claiming that they saw the creature move between Sky and the Doctor, when in fact it was not visible. Even Jethro begins to fall for these misguided claims and watches as Biff moves to throw the Doctor out of the capsule, at Sky’s command.
Dee Dee and the Hostess protest as the Professor joins in. Jethro finds himself torn between believing Sky and believing Dee Dee. As Biff shouts at him he begins helping to move the Doctor, who is doing his best to grab hold of the seats and save himself, all the while blindly repeating the words of Sky, who calmly eggs the others on.
However, when Sky says “allons-y” and “molto bene”, the Hostess realises from her conversation with the Doctor shortly before the capsule departed that Sky is using his voice and his words – Dee Dee was right. As the Doctor is dragged to the rear door she grabs Sky and takes her to the door that once led to the cabin. She opens it and after six seconds the pressure field gives way, sucking them both out into the radiation-washed landscape outside.
As the door closes automatically the Doctor drops to the floor and breathes deeply – he has been released. The other passengers recoil in horror at what has happened and as the Doctor struggles to regain his balance and composure Val is left alone with her indignant claim that she knew Sky was to blame all along…
Twenty minutes later, the rescue vehicle is about to arrive. Everyone sits silently until the Doctor asks sullenly what the Hostess’ name was. Nobody can answer. Nobody knew.
Eventually they return and the Doctor is greeted by Donna, who has heard of what has happened. She asks if the creature is still outside the leisure palace, but the Time Lord has no answer, all he can do is warn the owners of the complex that they should leave and let the planet be silent again. Donna claims warmly that she cannot imagine the Doctor without a voice and he smiles.
“Molto bene”, he says.
“Molto bene”, Donna replies, but the Doctor cannot smile at the friendly gesture. He tells her not to repeat him, evidently still unnerved by the creature lurking on the surface of Midnight.