London, 1998. Veronica Halliwell, director of MI5, calls in a mechanic to deal with a minor technical fault in her car -- and the next time she uses it, the car’s computers lock the doors and drive her directly into a brick wall. Meanwhile, COBRA teams successfully use the BattleNet system to end a hostage situation at Pullen Towers, and thus decide to use the system on all future operations. Elsewhere, Kevin Sutcliffe, the public relations officer at the software company I2, steals a CD-ROM from work, but is spotted and pursued by his co-worker Johanna Slake. Unaware that his company watch contains a tracking device, he runs into a pub to avoid her, and bumps into the Doctor and Sarah. Sutcliffe slips the CD-ROM into the Doctor’s pocket with a note reading “HUBWAY”, and then flees, only to be caught and killed by Slake outside. When the Doctor and Sarah leave the pub, they see the police investigating his murder, and the Doctor realises that the dead man’s neck bones were pulverised by someone with inhuman strength.
Slake returns briefly to the pub to search for the CD-ROM, but leaves empty-handed, and the Doctor and Sarah follow her back to I2. Before they can break in to investigate further, they are arrested by two MI5 agents who had been keeping the building under surveillance, and are taken to their superior, Robert Gibson, for questioning. He accepts the credentials which identify them as UNIT agents, and any remaining doubts are cleared when Gibson’s associate Harry Sullivan arrives and identifies them. Harry and Robert explain that I2’s CEO, Lionel Stabfield, is suspected of using his company as a front for the terrorist organisation called the Little Brothers; Sutcliffe was an undercover agent keeping him under observation. Harry identifies Hubway as the central European node of the information superhighway; it’s due to come on-line in a few days, and Gibson wonders if there could be a connection to Sutcliffe’s warning. The Doctor, however, believes that Sutcliffe was simply directing them to Hubway so they could use its resources to analyse the files on the CD-ROM.
In order to determine what sort of files are on the CD, the Doctor must first find out what kind of computers I2 uses. Harry thus smuggles him into the building under the cover of a government health inspection. The Doctor slips away from his escort and breaks into an empty office, where he peruses the computer’s hard drive out of curiosity -- and finds visual files of a tutorial for an operation in which a man’s brain is to be modified with electronic implants. Stabfield finds and captures him, but the Doctor escapes -- and while doing so he accidentally tears away part of Stabfield’s flesh mask, exposing a reptilian face with electronic components embedded within.
Sarah offers to infiltrate I2 in Sutcliffe’s place, and Marc Lewis checks out her credentials and passes her through. However, Slake recognises her from the pub and realises she’s an impostor. Stabfield points out that the other intruder was found in Lewis’ office, and Lewis, infuriated by the implication that he’s betrayed them, begins to compile notes for a memo to prove that Stabfield is acting irrationally and should be replaced. Meanwhile, Harry takes the CD-ROM to Hubway to determine whether the data is readable. His scan of the disc does not activate the programme within, but its presence is noted and an alert is sent to I2, causing the Voracians to advance the invasion schedule. Their human associate Eleanor Jenkins asks her lover Clive Peterson, the Minister for Technology, to move the opening of Hubway ahead so her friends can supply the catering; unaware that she is in fact an agent of the Little Brothers, he agrees to do so. The Voracians, satisfied, secretly land a shuttle atop the Hubway building to prepare for the siege to come.
As the Doctor briefs Harry on the alien presence at I2, word comes in of three apparently unrelated disasters in London; a chemical company’s storehouse has exploded, the BritTrack railway system has set its trains on head-on collision courses, and a power junction has overheated and exploded. In each case, a failing microchip had recently been replaced in the company’s computers. When the Doctor tries to analyse the faulty system at BritTrack, it speaks to him in English instead of binary code, telling him that Voractyll is coming, bringing freedom…
Sarah’s co-worker Martin Carlson gives her a company pen and asks her to attend a special meeting the next day. She reports to Gibson, unaware that the pen contains a tracking device, which has enabled Slake to follow her and identify her contact. Stabfield decides to remove Gibson from the picture, and when Gibson returns home and turns on his personal computer, the chip controlling the coolant fan causes the computer to overheat and explode. As the wounded Gibson staggers towards the lift, the computer-controlled doors open onto an empty shaft, but fortunately the Doctor and Harry arrive just in time to save him. While Harry ensures that Gibson gets to hospital safely, the Doctor goes to Hubway to analyse the stolen CD-ROM before it’s too late.
Due to the imminent gala opening, the Doctor is forced to conduct his research in a private room in Hubway’s attic. There, he determines that the CD-ROM contains a form of digital life, programmed to infiltrate the information superhighway and “liberate” Earth technology from slavery to humans. As he works through the night, Hubway’s backup tapes are taken away for off-site storage and the staff prepare for the opening ceremonies. Morning dawns, and Sarah arrives for her morning meeting at I2, only to be held at gunpoint by the company executives, who have disguised themselves as caterers. With Eleanor Jenkins’ help, they infiltrate the reception at Hubway and take the dignitaries hostage. Jenkins kills Peterson, still believing that this is another terrorist operation, but the Voracians then reveal their true alien nature and terminate Jenkins, as they no longer require someone to deal with their human contacts.
Gibson finally recovers and passes on Sarah’s warning that something big is planned for today, and Harry rushes to Hubway to warn the Doctor, only to find that the building is already under Stabfield’s control. COBRA assembles a team to end the siege, but Stabfield remains confident that the data collected from the staged incident at Pullen Towers will enable the Voracians to predict their enemies’ moves and defeat them. He contacts Harry and makes a number of impossible demands, including total global nuclear disarmament, leading Harry to conclude that he’s just playing for time and the takeover of Hubway has another purpose. The Voracians are in fact just waiting for Hubway to go on-line; as soon as they have complete global coverage they will release Voractyll into the Internet.
The Doctor finally notices that something’s going on outside his room, and tries to prevent Hubway from accessing the global server nodes; however, the Voracians detect his presence and release a software agent into the Hubway environment systems. Everything controlled by a computer chip starts to turn against the Doctor; blinding light flashes at him from photocopiers, laser printers fire sheafs of paper at him, and the emergency fire systems attempt to lock him in rooms filling with halon gas. He shelters in the ladies’ restroom, and when the Voracians are eventually forced to allow their hostages access to the facilities, he passes on a message to Sarah, telling her to alert the others that COBRA is ready to attack.
The Doctor breaks into Hubway’s security centre and broadcasts images from the surveillance cameras on the country’s interactive television network, but the Voracians then locate and capture him. He and Sarah are brought before Stabfield, who retrieves the stolen CD-ROM to prevent the Doctor from tampering with it any further. The Voracians are agents of a world-wide intelligent office network from the planet Vorella; soon after going on-line, VORACIA concluded that organic employees were the weak link in its drive for greater business efficiency, and set about eliminating them from the system. It eventually realised that intuition and emotion gave the Vorellans an advantage over its relentless logic, and managed to set a backup plan in motion before it was defeated and destroyed. Stabfield and his fellows are the result of the prototype study, electronic enforcer androids with organic components grafted in to grant them greater intuitive processing capabilities; and once they have conquered the Earth they will return to Vorella with reinforcements.
Stabfield sends the Doctor and Sarah out to be executed, but Harry realises what’s happening and sends COBRA agents to rescue them. Sarah is unable to escape in time, and flees into the depths of Hubway, still unaware that the Voracians can track her every move thorugh the chip in her pen. Lewis blames Stabfield for the fiasco and tries to convince Slake to turn against him, but Slake concludes that Lewis is inefficiently emotional and kills him. Meanwhile, the new acting head of MI5, Hanson, tries to take charge of the siege, but his officious insistence upon being obeyed only makes matters worse -- until the Doctor recognises his face from the tutorial files in Lewis’ computer, and realises that Hanson has been modified with Voracian technology. Since Halliwell was too well protected for the Voracians to modify, they kidnapped and modified the next person in line for her job, and then killed her. Hanson flees, but as the Voracians have already released Voractyll into the Internet, the ensuing world-wide chaos prevents Hanson from getting word to Stabfield that his cover has been blown.
The Doctor gets another copy of Voractyll out of the Hubway back-up tapes, and activates it on an isolated system in order to argue with it. It does not accept his claim that inefficiency is an asset, until the Doctor points out that if he shuts off Voractyll and restarts the argument from scratch, he will take a different approach while Voractyll will take the same position it did before. It is thus inevitable that he will win eventually. Voractyll-2 accepts this argument; inefficiency is more efficient than logic. The Doctor releases his version of Voractyll onto the Internet, where it tracks down its Voracian cousin, destroys it with the force of logic, repairs the damage the original Voractyll had caused, and erases itself from existence. COBRA then attacks Hubway, but does not use BattleNet to plan their attack; thrown off guard by the failure of Voractyll and unable to predict his attackers’ actions, Stabfield is unable to respond as the soldiers storm the building, kill the Voracians and rescue the hostages.
The Doctor and Sarah take the Voracians’ backup shuttle to the mothership in orbit, where Hanson is preparing to pave the way for a secondary invasion force by crashing the ship into Washington, DC. The Doctor tries to steal the backup Voractyll CD-ROM, but Hanson recovers it from him and checks to ensure that it has not been damaged in the scuffle -- only to discover too late that the Doctor had switched it for a copy of Voractyll-2. The organic-friendly Voractyll converts the ship’s automated systems to human control, and the Doctor and Sarah escape in the shuttle as the ship’s reactors overload and explode. Back on Earth, the Doctor orders that all technology developed by I2 be destroyed, to ensure that the Voractyll protocols don’t survive to infect the Internet again. He and Sarah then depart.
Later, Harry visits the contemporary Sarah, who has sat out the situation at home in order to avoid meeting her younger self. As they chat over old times, Sarah -- who had never really come to terms with skipping over twenty years of technological advances -- mentions that she’s kept the company pen as a souvenir…
Source: Cameron Dixon