Rose Tyler wakes up at 7:30, says, goodbye to her mother, and goes to her job as a clerk at Henrik's, a department store. She sits around all day and doesn't do much other than have lunch with her boyfriend, Mickey. As she prepares to leave at the end of yet another boring day, her co-workers ask her to take the accumulated lottery money down to the electrical engineer, Wilson, in the basement. Rose arrives there but can't find Wilson. As she looks for him, Rose hears someone moving around. Thinking it's Wilson, Rose goes to investigate but doesn't find anything but a room full of store mannequins. She steps into the room and the door slams shut behind her. Rose draws back in horror as the mannequins come to life and start surrounding her. However, before they can attack a man in a leather jacket bursts in and yanks her out. They run to the elevator and get in, but one of the mannequins tries to stop them. The newcomer yanks its arms off and the doors close and they ascend. Examining the arm, Rose realises that it's solid prank but still thinks it's some kind of student prank. The newcomer tells her that their attackers weren't mannequins... and Wilson is dead.
They get up to the store level and the newcomer uses a metal tube to somehow fuse the controls. He explains that the mannequins are alien entities being controlled from a relay point on the roof: a relay point he prepares to destroy. He gets Rose outside and tells her not to tell anyone what she's seen. He says that he's "the Doctor" and closes the door behind her. As a stunned Rose walks down the street, an enormous explosion envelops the roof of the department store. She heads for home through the gathering crowds, going past an old-style 1960s police box.
Rose arrives home to find Jackie watching the explosion on the nightly news. She suggests Rose get compensation and sell her story to the newspapers. Mickey arrives and invites her out to get a drink to settle herself down. She realises he just wants to go to the pub to watch the day's match on its TV, and tells him to go on his own. As he goes, she tosses him the mannequin's arm that she's still holding and suggests he get rid of. Mickey goofs around with it and then tosses it into a garbage bin as he goes. After he's gone, something moves inside of the bin...
The next morning, Rose gets up but no longer has a job for the foreseeable future. As her mother nags her about the lawsuit, Rose notices the cat flap rattling. She looks through it to see the Doctor on the other side. He says his tracker led him there and determines she's not made of plastic and Rose yanks him inside. Jackie wonders who he is but Rose says he's an investigator who wants to get her testimony. Jackie tries to flirt with the Doctor, who seems oblivious. While Rose makes coffee, the Doctor looks around the Tyler flat. He hears a noise behind the sofa and goes to investigate: the mannequin arm attacks him, trying to strangle him. Rose comes in and thinks he's joking at first, until the Doctor yanks it away and it attacks her. The Doctor finally manages to deactivate it using his sonic tube device. He prepares to leave with it and she demands answers. He says that he's just the Doctor, no real name, and the plastic creatures are after him. Rose is actually interested and the Doctor explains that the arm is controlled by thought waves and the controllers are still out there. She wonders who he really is and he says he's the one who understands what the world truly is. He tells her to go back to her normal life and forget about him. He walks toward a police box and there's a wheezing groaning noise. When Rose turns around, the Doctor and the police box are gone.
Rose goes to see Mickey and uses his Internet connection to do an online search. She finds a site with a photo of the Doctor and calls the site owner, Clive. She and Mickey go there and he insists on staying outside in the car. Rose meets with Clive, who is a relatively normal man with a wife and son, and a hobby of tracking the Doctor. As Rose goes inside to talk to him, Mickey notices a plastic garbage bin approaching his car... seemingly on its own. He looks inside but there's no one there. However, the plastic seemingly melts and attaches itself to his hands. He tries to pull free but it yanks him inside. The lid closes and the bin emits a loud belch.
Clive shows Rose his rose garden and the shed where he keeps a collection of articles about the Doctor. One is from the Kennedy assassination, one from the dock of the Titanic just before it departed, and one found in Sumatra after the eruption of Krakatoa. Clive warns that wherever the Doctor is seen, death and disaster strike at everyone he meets. Clive believes the Doctor is an immortal alien but Rose refuses to believe such a thing. She runs out to the car and tells Mickey that Clive is nuts. Mickey simply smiles at her, his face having acquired a smooth plastic sheen.
The couple go to a restaurant and Rose wonders what she's going to do with her life. Mickey keeps asking her about the Doctor. Rose isn't interested but Mickey persists, and the waiter offers them champagne. It's the Doctor, and he fires the cork directly into Mickey's forehead. It embeds itself and then bounces out: "Mickey" is made out of plastic. The replica attacks the Doctor, who manages to yank its head off. Unaffected, the replica continues its attack. Rose sets off the fire alarm to get the patrons out, and then she and the Doctor run out the back of the restaurant. The Doctor uses his tube device, a "sonic screwdriver," to seal the door shut but the replica begins hammering it down. The only other way out is locked but there's a blue box in the back courtyard. The doctor goes inside and Rose reluctantly follows him... and then backs out, shocked. The replica is almost through and she has no choice but to go into the police box... which contains an enormous control room many times larger than the exterior.
The Doctor takes the replica's head and wires it into the central console. He explains that the police box is a TARDIS, he can use the head to track the alien control signal, and he is in fact an alien. Rose is upset that Mickey must be dead if an alien took his place, but the Doctor seems unconcerned. However, she notices that the replica's head is melting. The Doctor starts working the controls to find the signal and the TARDIS shakes back and forth. He loses the signal before they can fully arrive and he stalks outside. Rose follows him and discovers that they've moved through space and are on the banks of the Thames.
The Doctor is still unconcerned about Mickey, saying that the Nestene Consciousness is responsible. It's feeding grounds were destroyed in a vast war and it plans to feed on Earth's toxin-rich atmosphere. The Doctor has a tube of "anti-plastic" to combat the Consciousness, but no way to track it now that the head has self-destructed. He says they need to find the transmitter, which would be a giant dish or wheel. As he rambles on, Rose finally gets his attention and directs him to the nearby London Eye. The Doctor realises it's exactly what the Consciousness needs and they go to investigate. Rose finds an access tunnel entry and they go below to find an enormous pit filled with liquid plastic: the Nestene Consciousness.
The Doctor demands a parley under the rules of the Shadow Convention and the Consciousness agrees. Rose finds Mickey, still alive, and cowering in terror. The Doctor casually explains that she knew that Mickey was kept live to sustain the replica. He's more interested in speaking with the Consciousness. He tries to defend Earth's right to survive but two mannequins grab him. They find the tube of anti-plastic, and the Nestene shows them the TARDIS, which its minions have brought to it. The Doctor defends himself, saying the anti-plastic is only an emergency measure. He insists he did what he could for the Nestene during the war but it's unimpressed. It identifies him as a "Time Lord" and begins its invasion, sending out an activation pulse.
Rose tries to warn her mother via cell phone without success because of interference. Jackie is visiting the Queens Arcade shopping centre and Clive and his family are there as well. They look on in horror as the mannequins in the store displays come to life, smash their way out, and attack the pedestrians. One of them ruthlessly guns down Clive with a built-in hand blaster. Everyone flees outside only to find more mannequins killing anyone in sight. Jackie hides behind a car but three mannequins in wedding dresses advance on her.
The ceiling collapses due to the activation signal and Rose and Mickey are unable to escape. Trapped with no access to the TARDIS interior, and with Mickey cowering in fear, Rose realises it's up to her. She uses an axe to cut free a chain and swings at the mannequin holding the anti-plastic. It drops the tube and falls into the pit. The Doctor breaks free and throws the anti-plastic into the vat. The Nestene howls in pain and starts to explode. The Doctor, rose, and Mickey escape in the TARDIS as the entire underground facility collapses in on itself. The mannequins, including the three preparing to kill Jackie, collapse now that the Nestene Consciousness is destroyed.
The Doctor materialises the TARDIS in a back alley and Rose confirms via cell phone that her mother is alive. Mickey cowers behind a pile of garbage as the Doctor admits that Rose saved the day. Impressed, he suggests that Rose travel with him. She decides she needs to stay to take care of her mother and Mickey. The Doctor quickly departs and the TARDIS dematerialises... only to reappear a few seconds later. He pops out to say that his ship can travel in time as well as space. Convinced, Rose kisses Mickey and thanks him for doing nothing, and goes into the TARDIS.