The TARDIS On Fire

With the TARDIS out of control, after his travelling companion Donna Noble accidentally spills her coffee over the TARDIS console at the end of the previous story "The Star Beast", the TARDIS crash lands in an apple tree - under which is Isaac Newton just at the point of reaching his famous epiphany of discovering gravity when fruit start to fall to the ground around him. They ask him what year it is, and from his answer of 1666 they figure out his identity. Donna is delighted, in spite of the fact that that TARDIS is going haywire, and insists on making a joke about the gravity of the situation, that she and The Doctor find themselves in. They then depart leaving a bemused Isaac Newton.

After their encounter with Isaac Newton the TARDIS then lands in a large and apparently empty spaceship. The Doctor places his sonic-screwdriver into the TARDIS key-hole, in order to prime the time machine to heal itself from the damage it has sustained. The Doctor and Donna start to take a look around the spaceship before hearing the sound of the TARDIS dematerialising. On returning, to where they left the TARDIS, they discover to their dismay that it has disappeared. The Doctor tells Donna the TARDIS has reset its numerous functions, including its HADS, the Hostile Action Displacement System, and that it will only return once they have resolved whatever danger they are about to encounter. The two set off into the spaceship with renewed determination, marching down a long corridor. As they walk a loudspeaker blares out with an unrecognisable word and the environment shifts around them. However, neither The Doctor or Donna understand what this announcement means as they can no longer rely on the TARDIS to translate for them.

They soon come across a small hover-vehicle and a slow-moving robot, that The Doctor names ‘Jimbo’, who is slowly moving down the spaceship's long corridor. Using the hover-vehicle the pair find their way to a cockpit where The Doctor tries to decipher what he can from the spaceship's computer. He discovers that there are no life signs on board, and the airlock had been opened once three years ago. The Doctor realises that the spaceship has fallen through a wormhole and has ended up on the very edge of the universe where there are no stars and no signs of life. The intercom then blares out with another unrecognisable word and the spaceship shifts again. In a side room they discover it is filled with drawers of baseplate repetition filaments. The Doctor asks Donna to move all the ones in a lower drawer to a higher one - the spaceship is on idle and needs to be powered back up. Leaving Donna to her task, The Doctor finds another room with a spindle and works on adjusting it. As Donna moves the filaments it grows colder, which she murmurs about. The Doctor, back in the room with Donna, acknowledges the change in temperature to her. And as the two talk The Doctor starts to mumble about his arms being too long.

Repairing The TARDIS

However, unknown to Donna, The Doctor actually is still back in the room with the spindle and is still working on adjusting it, he to notices it growing cold as Donna enters. He is surprised at how fast Donna was able to complete the task that he left her to do. As the two talk Donna comments that her arms are too long. The Doctor turns to look at her and sees her arm to be stretched beyond all proportion. The Doctor instantly realises that this isn't the real Donna. And with the real Donna, realising that it is not the real Doctor that she has been talking to, they both run, from their separate rooms, back to each other, with their doppelgängers slowly following behind. The Doctor realises that the doppelgängers are intelligent, but lack the concept of size and shape and constantly distort and morph into animalistic versions of them. Claiming to have come from nothing, to be Not-Things, they chase The Doctor and Donna, who use the hover-vehicle to try and outpace them, but the Not-Things grow and twist in size, keeping pace with The Doctor and Donna, before eventually tangling together and blocking each other and the whole of the corridor.

As the Not-Things slowly begin to untangle themselves The Doctor and Donna climb upwards to a vent. But when the intercom blares out again the environment shifts resulting in the two of them becoming separated. As the two walk around separately, trying to find the other, both pairs of The Doctor and Donna unite. The four try to convince their partners that they are real. But both of the Not-Things make mistakes enabling the real Doctor and Donna to flee again, with the Not-Things in pursuit, when the intercom once again blares out with another unrecognisable word.

Stranded

The four find themselves together in another room, and The Doctor and Donna figure out which of them is real by knowing enough about how the other acts. As the Not-Things begin to advance, The Doctor lays down a line of salt, insisting that they can't cross it until they have counted every grain. At first the two Not-Things are dismissive, saying it is just a superstition. But The Doctor insists, it is a superstition, and real, both at the same time. The Donna Not-Thing bends down and begins to count as they interrogate The Doctor Not-Thing, who they notice is slowly acclimatising. The Doctor Not-Thing explains that they have heard the ‘noisy, boiling universe’, and wish to venture there to play the games those in the universe do, that have given shape to the Not-Things. The Donna Not-Thing realises she has been duped and so blows away the salt, and the duo advance as the intercom blares again.

The Doctor and Donna run back to the spaceship’s cockpit and manage to lock themselves in, the Not-Things standing outside, slowly copying them more and more as the pair stresses and thinks. In order to combat this The Doctor and Donna try to think as little as possible, but they find themselves unable to do so - the spaceship just has so many unanswered questions. They then hear a banging outside and The Doctor realises that this is what was the captain of the spaceship. Still tethered what was the captain is bumping against the outside the spaceship. The Doctor realises that whoever opened the airlock three years ago was not entering the spaceship but was exiting so as to escape from the Not-Things.

The Doctor explains to Donna that the spaceship’s captain, to stop the Not-Things from reaching the rest of the universe, committed suicide three years ago by ejecting herself into space after setting off a series of actions so the Not-Things could not figure out what she had done. He correctly deduces that the spaceship has been very slowly reconfiguring itself into a bomb and that the strange words they have being hearing is a countdown and the robot they encountered in the corridor is slowly moving towards a self-destruct button in a last-ditch effort to kill the Not-Things. As the intercom blares out again all four of them race to stop the robot triggering the bomb. The Doctor speeds up the countdown to prevent the Not-Things from stopping the self-destruct. But The Doctor Not-Thing gives up on trying to copy The Doctor and becomes quadrupedal in order to reach the robot first.

Jimbo

Then both The Doctor and Donna hear the sound of the TARDIS returning and The Doctor realises that the danger it had sensed when they arrived is being resolved and the TARDIS is about to re-materialise. With the TARDIS returning they can finally understand how far the countdown has reached as the intercom blares out with the number ‘One’. This leaves The Doctor very little time to determine which Donna is real but is able to pull her into the TARDIS once she answers his questions to his satisfaction.

Still aboard the doomed spaceship, as the TARDIS dematerialises without her, the real Donna is devastated, insisting that The Doctor has chosen the wrong one, that she is the real Donna. With the TARDIS no longer able to translate the intercom once again blares out with an unrecognisable word. At which point the robot pushes the detonation button and the spaceship begins to destroy itself with the explosion rushing down the corridor to meet a distraught Donna.

Inside the TARDIS, The Doctor turns to face who he thought was Donna. But after noticing that her wrist is slightly too thick, and unbeknown to the Donna Not-Thing he pilots the TARDIS back to the spaceship to rescue the real Donna. On arrival The Doctor ejects Donna Not-Thing as the relieved, real Donna rushes in. The TARDIS instantly dematerialises and is seen flying away from the exploding spaceship that kills both Not-Things trapped onboard.

The TARDIS returns back near the alley from which they took off in London but The Doctor and Donna discover it is a day or two off. On exiting the TARDIS they discover Wilfred Mott who says that he never lost faith that The Doctor would come back to save them. Confused by this strange welcome The Doctor and Donna look around as small explosions and riots break out around them. They then witness a passenger aircraft flying very low above them. The Doctor, Donna, and Wilfred take cover against the TARDIS as the plane crashes nearby and explodes. Wilfred Mott is emphatic; the entire world is coming to an end and The Doctor needs to save them...