The three Ood advance towards Jefferson, his guard and Rose. Jefferson gives the order to open fire on the Ood, killing them. In the control room, Zack announces that the planet's orbit is stabilising around the black hole again. Danny reaches the others, warning them that the rest of the Ood are on their way. The pursuing Ood kill the female guard with a translation sphere before Jefferson opens fire again.
Zack finds himself trapped in the control room, as Jefferson reports that he is low on ammunition. Zack himself only has a bolt gun with a single bolt left. Jefferson recommends "Strategy 9"; Zack agrees, and tells him to get everyone together. To Rose's relief, the Doctor and Ida manage to contact the base. The Doctor reports that the seal is open, but nothing has come out of the Pit, which seems to be bottomless.
Zack orders Ida and the Doctor back up because of Strategy 9, but Ida is reluctant and asks the Doctor what he thinks. The Doctor muses about the curiosity he and humans feel about going down into the Pit, but notes that the Beast said he was "the temptation" — perhaps that curiosity is what the Beast is relying on. The Doctor suggests they retreat.
Jefferson aims his rifle on Toby, but Rose stops him from killing the now normal-looking and terrified archaeologist. They see whatever was possessing Toby pass from him to the Ood. Toby cannot remember much of what happened, but believes it was the Devil.
Down below, Ida explains that Strategy 9 is to throw open the airlocks while everyone else is safe in lockdown; the Ood will be sucked out into the vacuum. However, as they prepare to be brought up in the lift, the power fails. The Beast, speaking through the Ood, takes control of the viewscreens. To the Doctor's question as to which Beast he is, given that there are so many religions, the voice answers that he is all of them. The Beast explains that the Disciples of the Light defeated him and chained him in the Pit for eternity, before the creation of this universe. The Doctor retorts that this is impossible, but the Beast tells them that they know nothing, pointing out that the Doctor's belief is merely his version of a religion. The Beast begins to speak to each of them in turn, playing on their secrets and hidden fears and insecurities: to the Doctor, he refers to the Time War, calling him the "killer of his own kind", and ominously predicts that Rose will soon be lost in battle.
The humans begin to panic, but the Doctor tries to calm them by reminding the group of the strengths of the human race, demonstrated by their defiance of conventional belief in even making it to this impossible planet, and pointing out that they are united while the Beast is alone. As if in response, the lift cable snaps, and the Doctor and Ida barely get away before the ten mile-length of it collapses on top of the capsule, severing communications. They are stuck down there, with just fifty-five minutes of air left. Ida decides to rig up the loose cable so she can explore the Pit, but the Doctor tells her that he will go down, not her.
With the power loss, Zack is unable to implement Strategy 9. Meanwhile, the Ood are trying to break through the sealed doors to reach the humans. Rose rallies them, getting them to think of a way out. Zack reroutes energy from the rocket to restore half power. Danny comes up with a way to disable the Ood: broadcasting a telepathic flare that will reduce their telepathic field to zero, disrupting their brains. However, this can only be done from the central monitor in Ood Habitation. The only access from where they are is through the airless maintenance shafts below the base, but Zack can extend the oxygen field to follow them through the tunnels.
Danny creates and stores the flare programme on a memory card and they scramble down into the tunnels just as the Ood break through the door. Zack directs them towards their goal, aerating each section and decompressing the previous one before they can go through. However, the Ood are also in pursuit. Jefferson stays behind to hold them off, but is too slow in reaching a junction before it is sealed. Knowing that there is nothing Zack can do to prevent his death, Jefferson requests that the oxygen be removed quickly so he can die before he is killed by the Ood. Zack does this, and Jefferson's life signs wink out on the monitor.
However, the humans have little time to grieve, as the next section is also filled with Ood, and the others have to scramble up into the corridor above. The Ood almost reach Toby, but suddenly his eyes turn red, like when he was possessed by the Beast before. He places his finger on his lips signalling the Ood not to attack him or reveal his secret. The Ood pause, allowing Toby to be "rescued" by Rose and Danny, who did not notice the momentary change. As the others reach Ood Habitation, the Ood break through into the control room, and Zack holds the bolt gun on them. At the last moment, Danny manages to activate the flare; the telepathic field drops to "Basic Zero", and the Ood grab their heads and collapse. Zack joins them back at the mine shaft.
Meanwhile, the Doctor continues his journey into the darkness of the Pit. He tells Ida how the Devil crops up on so many planets in so many religions — perhaps that is what the Devil is, in the end: an idea. The line finally runs out, with still no bottom in sight. Preferring exploration to waiting for death, he decides to detach the cable and fall the rest of the way, despite Ida's pleas that she does not want to die alone. Reassuring her, the Doctor falls and vanishes into the shadows just as the others regain communications with Ida. Rose is grief-stricken when Ida tells them that the Doctor has fallen.
Zack tells Ida that there is no way to get to her, and Ida understands. All they can do is abandon the base and make sure no one comes back here. Rose wants to stay as well, but Zack renders her unconscious and carries her along; he has lost too many people. They make their way to the rocket past the bodies of the Ood, which are beginning to stir, their telepathic field reasserting itself.
Down below, the Doctor awakens. The faceplate of his helmet is smashed, but he discovers that he can still breathe; an air cushion must have supported his fall. Rose regains consciousness just as the rocket begins to launch. Despite her protests, and even when she threatens Zack with his bolt gun, Zack tells her that it is too late to turn back. Toby seems unusually amused that they have escaped, and when Rose begins to question the relative ease with which they managed to escape the planet, given the various ways the Beast could have killed them, he reprimands her questions with uncharacteristic viciousness.
The Doctor finds ancient drawings on the walls depicting the story of a battle against the Beast, his defeat and subsequent imprisonment. The drawings also depict two double-handed jars, which are standing on separate pedestals some distance apart in front of him. He touches one and they light up, illuminating a section of the cave. The Doctor comes face to face with a gigantic demon chained to the cavern wall, complete with caprine head and humanoid body.
The Beast who previously communicated with the Doctor was intelligent and vocal, but the creature now towering before him appears to be little more than animalistic in nature. The Doctor deduces that what he is seeing is only the physical form — the mind, the idea of the Devil, has departed. The Doctor also realises, piecing it together from various clues, that the planet was the perfect prison: if the Beast had ever freed itself, the gravity field keeping the planet balanced would collapse, and the planet would fall into the black hole. The air was not provided by the Beast, but his jailors, so the Doctor could stop his escape by destroying the prison and thus the planet.
The Beast has prepared for this: the loss of the gravity field would also mean the rocket would fall into the black hole, sacrificing Rose. However, the Doctor tells the Beast's body that the Beast's plan implies that Rose is a victim. The Doctor adds that he has seen a lot of the universe, and various beings calling themselves gods, but out of all that, if there is one thing he believes in, it is her. With that, he smashes the jars, causing the gravity field to collapse. The rocket shakes, turns and begins to be dragged into the black hole along with the planet.
The body of the Beast writhes, flames bursting from its skin. On the rocket, the runes appear across Toby's skin as the Beast takes full possession of him. He breathes fire and angrily defies death, ranting that he can never be destroyed. Rose grabs Zack's bolt gun and aims it at the cockpit's front window. Saying "go to Hell," she fires, shooting out the glass. As the air rushes outward, she unbuckles Toby, who is immediately sucked into space towards the black hole. Zack raises the emergency shield, but they are still falling towards the black hole. In the base, as the planet now hurtles towards the black hole, the Ood, now free from the Beast's control, huddle together nervously. Near the Pit, Ida slowly falls to the ground, the last of her oxygen exhausted.
As he stumbles away from the Beast's burning body, the Doctor finds the TARDIS in the collapsing cavern. The rocket crew watch the planet vanish, and brace themselves for death. Suddenly, everything becomes still, and to Zack's amazement, the rocket turns and heads away from the black hole. To Rose's delight, the Doctor's voice comes over the speakers, telling them that the TARDIS is towing them away. The Doctor was also able to pick up Ida — who will be fine aside from a little oxygen starvation — but unfortunately had no time to save the Ood.
The Doctor and Rose are joyfully reunited in the TARDIS once the rocket reaches clear space. Back on the rocket, Ida asks the Doctor what the Beast really was, and the Doctor replies that whatever he was, they beat it, which for him is enough. He assures Rose that when the Beast said she would die in battle, he lied. The Doctor tells Ida that perhaps they will see each other again. Before the TARDIS dematerialises, Ida asks who they are, and the Doctor tells her, "the stuff of legend."
Heading back to Earth, Zack dictates the final report of Sanctuary Base 6, recording the names of those who died with honours, beginning with Toby and continuing with the Ood.
Doctor David Tennant (Tenth Doctor)
Companion Billie Piper (Rose Tyler)
Danny Webb – John Maynard Jefferson
Shaun Parkes – Zachary Cross Flane
Claire Rushbrook – Ida Scott
Will Thorp – Toby Zed
Ronny Jhutti – Danny Bartock
Paul Kasey – The Ood
Gabriel Woolf – Voice of the Beast
Silas Carson – Voice of the Ood
Writer Matt Jones
Director James Strong
Script editor Simon Winstone
Producer Phil Collinson
Executive producer(s) Russell T. Davies
Production code 2.9
Series Series 2
Length 2nd of 2-part story, 45 minutes
Originally broadcast 10 June 2006