The TARDIS arrives in the year 200,000 aboard Satellite 5 and the Doctor, Rose, and Adam step out. Satellite 5 is orbiting Earth and Adam faints from the shock. Once he recovers, they go around the station and the Doctor is puzzled by the fact there are only humans aboard the station despite the fact there are hundreds of alien species in this era. He goes off to check up on the discrepancy and leaves Rose and Adam with a credit chip to make their way about.
The Doctor passes himself off as a manager and talks to two people, Cathica and Suki, who reveal that the entire satellite is devoted to broadcasting the news, and that all staff dream of being promoted to Floor 500. Meanwhile, Adam uses Rose's modified phone to call back into the past and leave news with his family but no one is there. A klaxon goes off and the Doctor gets together with them while Adam pockets the phone. The Editor continues to watch the Doctor and concludes that he shouldn't be there.
The Doctor gets into a management meeting with Cathica and all the reporters reveal there is a metal port on their head that allow them to link into information and Cathica is the central processor. The Doctor is suspicious and the Editor detects that there is a security breach. He identifies Suki as the liar and breaks the processor link. The Editor looks up to the ceiling and explains to a mysterious superior that they are working on the problem. Then he "promotes" Suki to Floor 500 but Cathica notes that no one who goes there ever returns. Adam bows out claiming he needs to acclimatise and Rose gives him a TARDIS key. Adam walks off, smirking.
Suki arrives on Floor 500 and finds it deserted and frozen. She wanders around and finds a number of shrivelled corpses. She eventually finds the Editor's room and she introduces herself and then explains that she has a fake biography and is actually the last member of a freedom fighter group. She pulls a gun on the Editor and demands to know who the Satellite's controller is, stating that facts have been manipulated. He refers her upward and they look to the ceiling, where some creature above lurks and drops on her as she unsuccessfully shoots it with her gun.
Adam gains access to a computer port and asks for information on microprocessors from his future. The Doctor asks Cathica for answers but she doesn't know much and she realises that they are not management staff. The Doctor points out all of the inconsistencies that Cathica has not even noticed, and concludes that the Earth's development has been set back at least 90 years – the time at which Satellite 5 began broadcasting.
Adam leaves another message on his answering machine in the past and starts transmitting information from the computers. But the Satellite computer stops and redirects him to Floor 16. He goes there and finds a medical lab, and a nurse tells him he needs a chip for further access to the computers. He opts for the Type II chip once he realises the Doctor's credit chip has unlimited funds.
The Doctor, Rose, and Cathica sneak into the station mainframe while the Editor watches them and is fascinated by the Doctor's lack of existence in the security files. A now zombie-like Suki follows his orders while Cathica starts to panic, wanting nothing to do with them. They comment on the intense heat within the station, and deduce that a large amount of heat is being vented away from floor 500. The Doctor accesses the system, apparently unaware that the Editor has allowed him entry. Meanwhile Adam gets his chip and is told that he can activate it by clicking his fingers.
The Doctor and Rose go up to Floor 500 and find it frozen. They make their way to the Editor and see that Suki is dead and has been slaved into the computer systems. The Editor wonders how they can exist without any record and has them taken prisoner. He reveals that humans are only allowed to exist on behalf of his employer, which is lurking on the ceiling. The Satellite's owner is the Mighty Jagrafess of the Holy Hadrojassic Maxarodenfoe (or "Max"), and intends to create a climate of fear to keep the borders closed and humanity enslaved. When they use the data ports and find a human that has caught on, the editor has them "promoted" and eliminated from the system.
Cathica has decided to access Floor 500 and uses the key code from earlier to go up in the lift. She makes her way into the control room while the Editor admits that he works for a consortium of banks who want stability among humans. The Doctor notices Cathica and mentions how Satellite 5 is a life-support system for the Jagrafess, which needs to be refrigerated.
Adam has made his way back to the computers and transmits the information from his port through the telephone back home. When he does so the Editor gains knowledge of the Doctor's background from what Adam knows and realises that the Doctor is the last Time Lord. The Editor plans to drain the knowledge from the Doctor's head and use his time-travel information to alter history to their benefit.
Cathica goes to the Floor 500 control room and uses her port to break the connection with Adam. The station starts to heat up and the Jagrafess overheats as the station goes into a panic. Rose breaks free and then releases the Doctor, while the Editor tries to escape without success when the Suki-corpse grabs him. The Doctor and Rose run while the Jagrafess explodes, taking the Editor with it.
The Doctor releases Cathica from the information spike and slips off quietly, but not before explaining that now humanity is back on track. The Doctor confronts Adam and hauls him into the TARDIS. They take Adam back to his house and the Doctor confronts Adam over his plan, destroying the information on the answering machine. A furious Doctor snaps his finger to reveal Adam's port and berates him about trying to alter human history. He warns Adam that he'll have to stay out of trouble because if someone finds out about the port they'll dissect him. They leave as Adam's mother arrives and mentions Adam has been gone for six months. She snaps her fingers at how much time has passed … and looks on in horror as the port on Adam's head opens…