The TARDIS materialises in a storage area on some sort of base. The Doctor and Rose wander through some corridors, not finding anybody. They do hear the voice of the base's computer though, which announces whenever a door is opened or closed.
The two of them enter a canteen area, and Rose notices the words “Welcome to Hell” written on a wall. Underneath it are some strange symbols.
The Doctor examines them and remarks that it's strange that the TARDIS isn't translating them. For that to happen would make the writing very old, even impossibly old.
The Doctor opens a door, and encounters a group of aliens. He tries talking to them, but they walk towards the Doctor and Rose repeating, “We must feed”.
The Doctor and Rose end up backed into a corner, but it turns out that there was a malfunction the ball devices the aliens use to speak, and what they meant was, “We must feed you.” Another door opens, and Jefferson, the head of security, enters.
Jefferson uses a communication device to tell the captain that they have visitors, who are “real people”. The captain doesn't believe him, but before they can have any further discussion, another voice appears and says that a bit quake is on the way.
As the base starts to shake, Jefferson leads the Doctor and Rose to the control room, where the rest of the crew is. Everyone is surprised not only to see the Doctor and Rose, but also that the two of them have no idea as to where they are and what's going on.
The captain, Zach, warns everyone that the quake is coming, and the control room shakes even more violently, and a console explodes. Zach does a quick check, and everyone says that they're all right.
He tells the crew that he was able to deflect the quake onto Storage Five through Eight, which they've now lost completely. Toby, one of the crew members, is sent by Zach to check on the rocket link, even though it's not his department.
After he's gone, the crew are introduced, and the names and jobs given are: Ida, science officer; Zach, acting captain; Jefferson, security; Danny, ethics committee; Scooti, maintenance; and Toby, who had just left, archaeology.
Ida pulls a lever and a window in the roof opens, showing the Doctor and Rose where they are – in orbit around a black hole. The Doctor gazes at it incredulously, saying that it's impossible for them to be in orbit around a block hole, as they should be pulled in.
Elsewhere in the base, Toby is checking the rocket link. He hears a voice whisper his name, but can't see anybody whose voice in might have been.
Zach tells the Doctor and Rose that the planet is generating a gravity field which keeps it in orbit around the black hole and part of the field extends out like a funnel, which was how they were able to reach the surface of the planet. Their ship was nearly torn apart and they lost their captain, giving Zach an unwanted promotion, but they made it to the planet, although they have no idea how long the funnel will remain open, which means they could be trapped.
The Doctor comments that the field would take a phenomenal amount of power to produce, and borrows a calculator to work it out. Meanwhile, one of the aliens from earlier gives Rose something to drink.
She goes over to Danny to ask about the aliens. He tells her that they're called the Ood, and they're effectively a slave race who have volunteered for the position.
If they're doing it voluntarily, then I'd say they're actually servants rather than slaves, but Rose doesn't seem to consider that. She asks one of the Ood if it enjoys being ordered about, and it replies that it is all they crave as they have nothing else in life.
The Doctor has finished his calculations and determined that the power source needed for the gravitational field would require an inverted self-extrapolating reflex of six to the power six every six seconds. Amongst that bit of technobabble is a huge clue as to what's going on, but the Doctor seems to miss the significance of the three sixes. Ida explains that the power source is ten miles below solid rock, and the purpose of their mission is to drill down and find it.
Toby, who has returned to the control centre, tells the Doctor that there used to be a civilisation on the planet, long before the human race had even learned to walk. He goes on to say that he was the one who had written the strange symbols, which he had copied off some fragments they found when drilling.
The Doctor is full of admiration for them coming to the planet, but tells them that they're completely mad and need to get in their ship and leave. Ida asks why the Doctor is there, and he says that he has a ship which sort of appears.
Rose offers to show it to them, and she and the Doctor try to explain where it is. Zach says that they're talking about Storage Six, and the Doctor remembers what happened to Storage Five through Eight.
The Doctor runs through the base back to where they left the TARDIS. He reaches a door which is out of commission, and looks through the window. Outside is the surface of the planet, and they're at the edge of a large chasm.
The Doctor returns to the control room and tries to convince Zach to divert some of the drills to help him retrieve the TARDIS. Zach tells him that they don't have the resources to divert anything away from the shaft they're currently drilling, but he can offer the Doctor a lift if they ever do leave the planet.
That evening, Toby is working in his room when he hears the voice calling him again. He thinks it's Danny and tells him not stop playing around, but when he goes to look for the source of the voice, he doesn't find anyone.
The next day, the Doctor and Rose are in the canteen with some of the crew. Rose goes to get some food from one of the Ood, and talks to it, trying to share some of her experiences of being a dinner lady.
The Ood's response is, “The Beast and his Armies shall rise from the Pit to make war against God.” Rose is a bit puzzled, but the Ood then taps it's speech device and apologies, saying that it had said that it hoped Rose enjoys her meal.
Zach is busy working in the control room, where in front of him is a hologram of the planet. He turns to look at some more controls, and the image of the planet briefly changes to that of a horned demon.
This means that so far we've had three sixes mentioned together, a reference to “the Beast”, and an image of a demon. I think that should be enough to indicate what's going on here.
Elsewhere, Danny closes a door, and the computer voice announces that “He” is awake. Danny asks the computer what it just said, and it repeats its “close door” statement.
Toby, working in his room, hears the voice again. He starts to turn, but it tells him not to turn around as if he looks at it he will die.
The voice says a few more things, all the time interjecting with the command that Toby not turn around. Eventually he can't stop, and he does turn, but there's nothing there.
He looks down at his hands, and discovers that his palms are now covered with the symbols from the fragments. He picks up a mirror and looks at his face, to find that it's also covered with the symbols, and his eyes have turned red. He collapses unconscious on the floor.
Zach announces that the Scarlet Systems is burning up, and in the canteen Ida pulls a lever that opens the overhead window. Everyone watches as a red stream of light is sucked into the black hole. Ida tells them that it's all that was left of a civilisation that spanned a billion years.
The Doctor and Rose reflect on the fact that they're stuck on the planet. Of course, we know that's not true, as if there's one certainty about this show, it's that the TARDIS will never be gone permanently.
Rose checks her phone, and for the first time ever, there's no signal. She wonders if the Doctor would be able to build another TARDIS, and he says that that they were grown, not built.
They talk for a bit more, and then Rose's phone rings. She answers it, and the voice that has been haunting Toby says that “He” is awake. Elsewhere, a symbol-covered Toby wakes up.
The Doctor and Rose head down to the Ood Habitation, where Danny is working at a computer on a balcony above the Ood. The Doctor asks how the Ood communicated, and Danny says that it's a low-level telepathic field. Rose tells Danny about the Beast comment and the message on her phone, which Danny writes off as stray transmissions.
He goes on to say that they monitor the telepathic field. The Doctor identifies the monitor, which reads “Basic 5”, and Danny explains that's the Ood's telepathic level. As they watch, the level goes up to Basic 30.
The Ood down below all stand up and turn to look at them. Rose asks what Basic 30 means, and Danny says that they would be screaming inside their heads.
The Doctor asks Rose what the message on her phone said. When she says that it was “He is awake”, the Ood all reply with “And you will worship him”. The Doctor repeats Rose's message, and the Ood respond in the same way again.
Scooti enters Toby's room, looking for him. He's not there, and she hears the computer's voice announce that an airlock has been opened.
She asks the computer who went outside, but the computer can't confirm who it is. Scooti tries a different tack, asking whose spacesuit has been logged out, but the computer tells her that no spacesuit has been. Scooti continues to question the computer, but it tells her that He is awake and he bathes in the black sun.
Scooti looks out of the window, where she sees Toby out on the planet surface, without a spacesuit. He's still covered in the symbols and his eyes are still red.
Naturally, Scooti is bewildered at Toby being out there. Her bewilderment changes to terror as Toby raises his hand and clenches it into a fist, which somehow results in cracks appearing in the window.
Scooti runs for a nearby door, but it won't open. Eventually the window explodes, and Scooti is sucked out.
The computer announces a hull breach, and Zach orders an evacuation of the affected section. People head to the canteen, and the last person to make it in is Toby, his face now clear of symbols and his eyes a normal colour.
Zach asks for a report, and Jefferson says that everyone's there except for Scooti. Zach says that her bio chip indicates that she's in Habitation 3, and everyone heads off there to find her.
They reach Habitation 3, but there's no sign of Scooti. Jefferson and Zach argue for a bit about the computer indicating that she's there, but the Doctor finds her. Looking through the overhead window, they see Scooti's body floating in space.
They close the shutters on the overhead window, and once it's shut they notice that the base is quieter than usual. Ida says that the drill has stopped, which means they've reached their target.
At the shaft, Ida prepares to descend as the Doctor walks up, dressed in a spacesuit, to volunteer to go down as well. Zach is uncertain as to whether he should allow the Doctor to go down, but eventually gives in. The Doctor and Ida get into an elevator, which slowly begins to descend to the centre of the planet.
After a bit of a bumpy rider, the elevator reaches the bottom of the shaft. The Doctor and Ida exit and find themselves in a large cavern. Ida activates a globe which provides light, and they discover a large face carved into the rock.
Back on the base, Danny contacts Zach and tells him that the Ood are behaving strangely. They're staring at him, and the telepathic field is registering Basic 100, which means that they should be dead. Jefferson sends a member of security to keep watch on the Ood.
The Doctor and Ida come across a large metal disc, which they think is a trapdoor. They say that it's thirty feet in diameter, but something's gone wrong somewhere, because if the shot of the Doctor standing next to it is anything to go by, then for the trapdoor to be thirty feet in diameter, David Tennant have to be the tallest man who ever lived, by quite a large margin.
The Doctor says that there are symbols on the trapdoor which might tell them how to open it, and he asks Toby if he's had any success in translating them. Toby says that he knows exactly what was said.
Toby stands up, and reveals that he's back in symbol-covered mode. He speaks with the voice of the Beast that we've heard before, saying that the Beast has woken and will now rise.
Jefferson demands that Toby stand down and be confined. Toby responds by asking whether Jefferson's wife ever forgave him and then answers the question, saying that she never did.
Jefferson points his gun at Toby, saying that he's authorised to shoot Toby. The symbols on Toby's skin turn into smoke, which enter the nearby Ood. The Ood in the Ood Habitation area are also possessed, and they all announce that they are the Legion of the Beast.
While Zach and the Doctor call for reports over the communicator, the Ood continue talking, basically saying that Satan has been freed. That’s not much of a surprise given the clues I've already pointed out and the title of the next episode (The Satan Pit).
One of the Ood walks up to the guard with Danny, and the Ood's speech device flies out and attaches itself to the guard's forehead. The guard jerks a few times, as though he's being electrocuted, and then falls to the ground, dead.
The Ood with Rose and Jefferson begin to advance towards the humans, who back away. The base starts to shake, and Zach in the control room says that the planet’s moving.
On the surface of the planet, the trapdoor begins to open. Zach looks at his controls and announces that the gravity field has gone and they're falling into the black hole. Meanwhile, the Ood have backed Rose, Jefferson and another crew member against a door which they are unable to open.
The trapdoor finishes opening, and the Voice of the Beast can be heard. It says that the Pit is open and it is now free.
Quotes
Danny: They're the Ood.
Rose: The 'Ood'?
Danny: The Ood.
Rose: Well that's... ood.
Danny: Very ood!
The Doctor: There we go. Do you see? To generate that gravity field, and the funnel, you'd need a power source with an inverted self-extrapolating reflex of six to the power of six every six seconds.
Rose: That's a lot of sixes.
The Doctor: And it's impossible.
Zach: It took us two years to work that out!
The Doctor: I'm very good.
Toby: There was some form of civilisation. They buried something. Now it's reaching out. Calling us in.
The Doctor: And you came.
Ida: Well, how could we not?
The Doctor: So, when it comes right down to it, why did you come here? Why did you do that? Why? I'll tell you why. Because it was there. Brilliant.
The Doctor: I'd have to settle down. In a house or something, a proper house with... with... with... with DOORS and things. Carpets! Me! Living in a house! Now that... that is terrifying.
Rose: Don't forget to breathe. Breathing's good.
Ida: Well... we've come this far. There's no turning back.
The Doctor: Oh, did you have to? No turning back? That's almost as bad as "nothing can possible go wrong" or "this is is gonna be the best Christmas Walford's ever had"
The Doctor: We've found something. It looks like metal. Like some sort of seal. I've got a nasty feeling the word might be 'trapdoor'. Not a good word, 'trapdoor'. Never met a trapdoor I liked.