Kate Maguire and Lisa Henshaw, two teenaged schoolgirls, are playing truant from school so that they can visit Hyperville, the new ultra-modern shopping mall. It is the largest in Europe and full of high-tech devices like the floating spheres loaded with CCTV cameras. Kate is fascinated by the place and is even writing a project about it for her Cultural studies lessons. Her interest has been noted. In the control centre, Max Carson (Director of Operations) orders that she be tagged and followed. The girls' perambulations are interrupted when a stranger stops them and, for no apparent reason, gives Kate a futuristic version of the mall's Hypercard. He tells her it may come in useful in the future and then disappears into the crowd.

Several years later the TARDIS materialises in the mall's Holistic Zone. It is 2013 and the Doctor emerges and shuts the door by clicking his fingers. He looks around, simultaneously perturbed and impressed by the five square miles of shopping experience. He steps back for a better view and almost bumps into a small boy, Reece, and his teenage sister Chantelle. Overhearing that they are going to the Doomcastle the Doctor is intrigued and decides to join them. He uses his sonic screwdriver to claim a ticket from an electronic booth. The booth switches off after his transaction and in the control room Max Carson is alerted. Within seconds the security team have called up the Doctor's image and analysed the sonic wave that he used. Carson is delighted to have a proper, sophisticated criminal on the premises.

A journalist, Anrdrea Watkins, is waiting to interview Carson. She is led to an interior office and is introduced to Carson and the immaculately dressed Elizabeth Devonshire. Two heavily muscled security men are also present. Watkins, from writing a puff-piece about the mall begins by asking probing questions about the recent death on the premises of an electrician and wonders whether it has any links to Hyperville's recent investment in Plastinol-2. Elizabeth Devonshire reads through Watkins' notes and agrees that the death was suspicious. She asks what the journalist intends to do. When she is told that Watkins is preparing a devastating article she drily notes that the journalist is wearing Plastinol-2 boots bought from the mall. She turns the dial of her gold watch and the boots pin the journalist to the floor and spread up her body. Her skirt tightens and spreads, too. Carson looks nervously at Devonshire, saying that this was merely intended to scare the journalist but Devonshire simply smiles as the woman in front of her is totally engulfed by the material and her screaming stops.

In the rickety wooden train that is the Doomcastle ride the Doctor bumps into Reece and Chantelle again. He has noted that the ride can also take visitors through the whole mall. He sits near the children, their mum, Tricia, and the mum's boyfriend, Derek. The rest of the passengers seem to be family groups, too. The train, 'driven' by a plastic driver, accelerates away.

Meanwhile, four smartly dressed young men and women are in a lift with Sir Gerry Hobbes-Mayhew, Hyperville's owner. It is four years since Kate Maguire's schoolgirl visit and now she is one of the four young people that Sir Gerry has chosen to as Trainees. Leading them to his office he tells them that he wants them to spend the next few days getting to know the store and finding ways to improve it. They are introduced to Elizabeth Devonshire who gives them security passes and copious notes to read. They are also given a Hypercard each, already loaded with money, though Sir Gerry won't tell them how much. Sir Gerry sends them out to explore and tells them he expects a report from each of them in a few days.

The Doomcastle train lurches through dimly lit tunnels, passing skeletal figures and glowing ghouls. The Doctor is worried that it seems to be travelling too fast and makes his way to the locomotive at the front. He pulls two wires from a control panel and the engine stops; the train slows to a walking pace. Grabbing a plastic broom from an animatronic witch the Doctor jumps out and jams the broom between the wheels to halt the train. He tells the passengers that they will have to walk to the end of the tunnel. After the passengers have left the train, the Doctor examines the driver's plastic head with his screwdriver. He then leads the passengers down a torch-lit passage.

In his chair, Max Carson watches all of this with fascination. A voice in his ear calls him and Carson flicks a switch, dropping his chair several floors into the bowels of Hyperville where something is waiting for him.

Kate leaves her other trainees and heads into Hyperville with her Access All Areas badge. She chats to shop managers and security officers until she comes upon a promotional appearance by the pop singer Shaneeqi. She uses her pass to meet the singer and introduces herself as Sir Gerry's assistant. They chat about the singer's boyfriend, international footballer Paul Kendrick who is flying in from Milan. Kate also finds out that the singer will be appearing in Hyperville's FunGlobe later. This is news to Kate, as she has been locked in a hotel with the other trainees for two months. In order to ingratiate herself with the singer, Kate offers to find out what time her boyfriend is due to fly in.

The Doctor leads the passengers from the train down the Hall of the Doomcastle. An advanced animatronic vampire closes in on them and the Doctor disables it at once. The passengers leave by a nearby door while the Doctor takes one of the vampire's fangs and drops it into a specimen jar. Two witches on broomsticks promptly swoop down towards him.

In the maintenance tunnels two workers are confronted by two plastic dummies. Unnerved, they turn the other way and are cut off by a small girl with glowing red eyes who raises her arm and kills them both.

On the roof of the ShopZone Captain Tess Tilbrook waits by the helipad, reflecting on the high levels of security that operate within the mall. She watches a helicopter land and Paul Kendrick step out. She introduces him and leads him to the lift.

Kate introduces herself to Max Carson, seated in front of his monitors. He is watching the Doctor's confrontation with the two witches. Two knights have joined in and the Doctor is flinging himself around to avoid their swords. Kate pleads with him to stop the attack and Carson agrees, giving the order for the witches and knights to stand down. The Doctor hurries away to the exit from Doomcastle. He returns to the shopping area and is dismayed to find that the TARDIS has gone. Instead, Max Carson and two security men are waiting for him. The Doctor takes to his heels and disappears into the crowd.

He races down some stairs and nearly collides with a slim, attractive 20 year-old girl in a business suit. He shows her his psychic paper and she responds by tapping her badge, saying Kate Maguire, and pointing out that his paper is blank. She opens a nearby maintenance door and tells him to step inside, saying that if Max Carson has a problem with the Doctor then she intends to help him; he looks like a nose-poker to her and she is trying to find the truth behind Hyperville, too.

Out in the shops, Derek sees a small clothes dummy move. His data is immediately downloaded into a screen in the data core and his elimination is ordered. Meanwhile, on the edge of the solar system, a cluster of objects is approaching.

Kate has remembered her encounter with the Doctor, four years earlier, though she is keeping this to herself. Instead she is talking to him about Hyperville's imminent switch over to a new centralized computer program. She discusses the involvement of Miss Devonshire, the mysterious deaths and closures in parts of Hyperville. They emerge from the maze of tunnels into a snowy landscape where they are surprised to see a sleigh pulled by four reindeers approaching. The sleigh is carrying the Snow Queen.

In the Forest Zone Reece and Chantelle are rescued by security men when the Robin Hood and Marion robots try to kill them. Max Carson orders the children to be taken to a hospitality suite. Chantelle shouts that she will tell the papers about what she has seen but Carson replies that she won't be going anywhere in the foreseeable future.

In the WinterZone the Doctor and Kate are being pursued by the Snow Queen through a snowy forest scene. They run into another tunnel and emerge in the main atrium of Hyperville. Kate uses her security clearance to access the public address system and begins to clear the shoppers from the area. Security guards immediately surround Kate and the Doctor but their attention is distracted when the Snow Queen bursts from the WinterZone entrance. People scream and run for the exits. The Snow Queens hand drops forward to reveal a gun that shoots a bolt of red energy, which the Doctor reflects back with some plastic ice, blowing her head off. Captain Tilbrook arrives, saying that Sir Gerry wants a word with both of them.

Tricia Stanford leaves Derek in the lounge of their rented penthouse apartment while she goes to take a shower. In her absence the little dummy from the clothes shop enters, a one-metre tall girl dressed as a waitress. Chuckling quietly to herself she murders Derek. As this is going on Max Carson and a security team neutralize all of the rogue Autons with plastic discs. The only one they can't account for is the little one. Miss Devonshire tells him that this one needs to be neutralized too, before it causes any damage. She does not want to unleash the Autons until the Central Program is online.

At the same moment, the Doctor is telling Sir Gerry that he has seriously dangerous automata at loose in the various zones. He adds that the creatures are called Autons and are part of the Nestene Consciousness. He adds that this is the fourth invasion attempt at least and wonders why nobody ever seems to remember the first three. Sir Gerry refuses to believe him and also demands that the Doctor hand over the screwdriver he used to access the Hypercard machines.

The Doctor and Kate make their way through Hyperville. All the while he is checking a compass-like object for unusual readings. He tells Kate that the Casino, where Shaneeqi is due to perform, seems the most likely place for any trouble. While they walk, Kate explains how the Hypercard works to access a customer's account and debit money. The Doctor seems unenthusiastic about this advance in consumerism. He is impressed, however, by Kate's lack of fear about any impending danger. They see some guards in a hurry and decide to follow.

Elsewhere, Miss Devonshire tells Max Carson that he has twelve hours to get the Program ready, but before that there will be one final trial before the Nestenes rise up.

The Doctor and Kate arrive at room 776 of the Hyperville Hotel. Inside, six guards are standing around Derek's corpse. Kate persuades them to let the Doctor examine the room and he tells them that Derek was strangled by someone wearing a child's size twelve shoe. Captain Tilbrook wants to evacuate the whole of Hyperville but the Doctor thinks that would trigger a Nestene assault. He pulls out his sonic screwdriver to examine a ventilation duct, telling Kate that he gave Sir Gerry a portable immersion heater. He asks Tilbrook if there is anywhere in Hyperville that she can't access, where only Carson and Devonshire could go, but she says she doesn't know of anywhere like that. Then he asks her to look after Tricia and find out where her two children are.

The Doctor has not come to Hyperville by accident. He follows the readings on his detector as he wanders the store. He asks one shop assistant what the dummies are made of. She replies that it is Plastinol, just like anything modern. He heads off to an internet café to do some research. He finds that the new Central Program is due to go online at midnight.

He tells Kate this information when he meets her at the Shaneeqi reception in the casino. The singer is on stage with her footballer boyfriend. The needle on the Doctor's detector is pointing directly at the stage and the Doctor orders everybody to get down.

Max Carson had risen from Managing Director of a small firm making plastic when he was head-hunted by Miss Devonshire. His firm became a subsidiary of Hyperville Holdings and Carson realised his firm had become the front for a much bigger company with an interest in developing plastic beyond his imagining. With the promise of fabulous riches to come he had grabbed the opportunity with both hands.

Several things happen at once: the footballer points at the Doctor, saying that Carson had warned him the Doctor would be trouble; his hand opens to reveal an alien gun; Kate pulls Shaneeqi away to safety; Max Carson sounds a siren through Hyperville, on Miss Devonshire's orders; the Consciousness in level Zero howls; the cluster of spheres pass Jupiter, heading for Earth.

Captain Tilbrook tracks the small Auton girl to a clearing in the WinterZone. She orders it to halt but it attacks her so she shoots it full of bullets. To her horror the Auton grins as the bullet holes close up. The plastic snow around the Captain's feet melds together to hold her in place and begins to creep up her legs. The Auton leaps and starts to strangle her.

In the Casino the waiters and waitresses point at the guests, their hands clunking open to reveal guns. Kendrick advances on the Doctor who demands that the Autons let the people go. Kendrick tells him to listen to the sirens, saying that most of the people are leaving, save the few needed for training. An Auton waitress shoots a guest dead. Kendrick orders the crowd to run. As they do so the Auton footballer tells the Doctor to follow him to where Carson and Miss Devonshire are waiting.

In the Plaza, the guests from the Casino run for the exits but are massacred by witches and knights from the Doomcastle.

In the hospitality suite Chantelle and Reece are attacked by two Autons but Chantelle, thinking quickly, charges one and pours nail varnish onto its head, which begins to melt. She drops the bottle but Reece scoops it up and uses it on the other Auton. When the two Autons are defunct the children make their escape. They run through the deserted Megastore, only stopping for Chantelle to stock up on nail varnish and hairspray. They bump into Kate and Shaneeqi running the other way and realise that they are all looking for the Doctor. Chantelle notices that the shutters are down on the exits and they are sealed inside. Autons suddenly burst out of shop windows around them but start staggering about. Life sized baby dolls drop from the balconies above and advance on them. Into all this steps Sir Gerry, just returned from a business meeting. He looks around the mall with horror. Kate borrows his cigar lighter and a can of hairspray from Chantelle to create a flame thrower to set fire to the dolls. The party of five runs from the Autons who are now more sure-footed.

The Doctor is taken to Level Zero, a huge freezing cold space. The Doctor notes that Kendrick's breath mists the air while the two waitresses with him don't. Miss Devonshire and Max Carson stand in front of the bubble containing the Consciousness. To the Doctor's surprise they ask him to look at the Consciousness for him. He listens to the casing with a stethoscope and concludes that the Consciousness is dying. Carson tells him it fell to Earth thirty years ago and has been recuperating since. The Doctor says that the damage means the Consciousness cannot control the Autons. Miss Devonshire asks him to amplify the creature's distress signal so that it can be rescued. If he refuses, she says, she will unleash the Autons on mankind.

The Doctor asks to be given access to the warp-shunt interface. Miss Devonshire agrees but orders one of the waitresses to force Carson to his knees, saying he will be the first to die if the Doctor tries anything funny. The Doctor checks over the system before declaring that Miss Devonshire doesn't want to get the Consciousness into space, she just want more power to further her plans on Earth. He adds that he has accessed the Central Programme earlier in the day and added a trick of his own. Leaning towards a microphone he admits to talking rubbish. This last word causes the Autons to hold their heads and reel around while the Consciousness emits a deep, angry scream. The Doctor runs to the lift, followed by Max Carson. As they enter, Carson pulls out a pistol. He says he wants the Doctor to get him to the helipad on the roof so that he can make his escape but the Doctor warns him that his sabotage will only last thirty minutes or so and that he needs the time to end the Auton invasion.

The five fugitives use this diversion to escape into Wild West World and seal the door (dura-titanium) behind them.

The Doctor and Max reach the security centre where the Doctor uses the CCTV to find Kate and her new friends. Just as he locates the Nestene signal the little Beta-4 Auton shoots at him, destroying the console. Paul Kendrick enters behind her. Beta-4 knocks the Doctor down and holds him at gunpoint while the plastic footballer does the same to Carson. The Doctor talks to Kendrick, asking him what it feels like to have memories from the last twenty five years only to find that he is a plastic Auton, a new generation of lifelike creatures. He wonders if that was why Kendrick hesitated to kill in the Casino, despite orders from the Consciousness. He talks about how brilliant Kendrick is as a footballer, an inspiration to millions, and how none of that was Nestene created. Kendrick mulls this over, and as his gun arm drops Max Carson spoils it by shooting him six times. Kendrick reverts to his Auton personality, heals himself and kills Carson. In the confusion, the Doctor knocks away Beta-4 and reaches the fire door.

Elizabeth Devonshire connects with the Consciousness. Memories flood through her: finding the Consciousness in an abandoned industrial estate, returning to check on it every month, learning from it as she helped to build Hyperville. The Consciousness courses through her and she ripples like a green ghost. Her fingers grow like tentacles as she ascends.

The Doctor emerges in the Wild West World and finds the others in the town saloon. He quickly mixes a cocktail of spirits and drops the vampire fang from Doomcastle into it. It dissolves instantly. A noise outside alerts them and a phalanx of Autons burst onto the scene. He Doctor uses Kate's internet linked phone to send another migraine-inducing signal to the Autons. He uses the pause to jam his screwdriver into a sharpshooter's ear and makes some adjustments. He calls this one 'Joe Auton'. He then leads his unlikely party to the model steam train and sets off. On the way he tells Kate he wants her to find the main pipe source of the sprinkler system on the thirtieth floor and introduce his anti-plastic formula. He says it should replicate itself in the water. He needs to find Miss Devonshire first and give her the choice before he activates the fire alarms. Kate hands him a Hypercard, saying he will need it. She says she doesn't know why but the Doctor gave it to her four years earlier when she first met him.

The physical manifestation of the Nestene Consciousness, still bearing a resemblance to Elizabeth Devonshire, strides through Hyperville.

Kate and Shaneeqi climb the maintenance ladder in the lift shaft, leaving Reece and Chantelle to guard the doors. Beneath them, the lift begins to move. As it approaches, they jump onto its roof. Just then, a pinkish glow lights the singer's eyes and she apologises. Before the lift can crush them against the top of the shaft Shaneeqi reaches out and brings them to a screeching halt. She tells Kate she realises her whole life was an invention. She says she can only hold back the Consciousness for a few seconds and tells Kate to go. Kate climbs out of a hatch before the singer lets the lift rise up and crush her. The Doctor activates Joe Auton to hold him and Sir Gerry at gunpoint and lead them to the Atrium where the witches accompany them. They arrive in Europa Plaza where hundreds of Autons and Miss Devonshire await. She tells him there are seven minutes until activation. He tells her there is still time to stop but when she refuses he apologises. Sir Gerry and the Doctor drop to the floor and Joe Auton fires his sharpshooter pistol. A bolt of Nestene energy fires at Miss Devonshire and she deflects it back, blowing the sharpshooter's head off.

In space, the cluster of spheres hovers above the moon, ready.

Kate is still struggling to open the valve to the sprinkler system when Kendrick arrives and sends a bolt of energy at her which splits the pipe. She pours the anti-plastic in and presses the send button on her phone.

Water pours from all of the sprinklers and the Autons begin to dissolve. The Doctor fits the Hypercard into Chantelle's phone and types in a sequence of numbers. Before he can press 'send' the Consciousness knocks the phone from his grasp. Reece and Chantelle arrive and Reece picks it up. It begins to bend and melt in his hand but he manages to press the right button.

Above the moon, the cluster of spheres becomes inert and they crash, lifeless, to the surface.

The thing which had been Miss Devonshire shrivels and dries. Green froth pours out until the creature bursts and dies.

The next morning Sir Gerry discusses how he is going to renovate the mall. Kate suggests an eco-friendly complex using recycled and renewable materials. Sir Gerry is enthusiastic and says this could be the start of a wonderful partnership. Kate excuses herself and makes her way down through the mall where UNIT are clearing up the Autons. The Doctor tells her he is leaving but Kate says he can't because all the exits are cordoned off. He steps into the TARDIS, saying he has got to get the Hypercard back to her sixteen year old self. To Kate's astonishment the TARDIS fades away, only to reappear seconds later. The Doctor saunters out saying that it was a time paradox but it would sort itself out in the end. He makes his farewells and the TARDIS disappears again.