Rose Tyler wakes up in the morning for another boring day in her boring job. She says goodbye to her mother, Jackie, and goes to the department store where she works. She meets with Mickey for lunch but the rest of her day consists of not doing much except waiting for her job to end. However, as she prepares to leave, the employees ask her to take their lottery money down to Wilson, the electrical engineer. He has an office in the basement but doesn't answer when Rose knocks. She hears someone moving around and follows the noise to a room full of department store mannequins. The door slams behind her and the mannequins come to life, advancing on her...
A tall man in a leather jacket bursts through the mannequins and pulls her to safety. He gets her to the elevator but as they get inside, one of the mannequins blocks the doors with its arms. The stranger yanks the arm off and tosses it to Rose, and they go up to the store level. Rose examines the arm and realises it's impossibly solid plastic. She wonders if it's some kind of student prank but the stranger assures her the mannequins are living entities of plastic, and they're controlled from a relay point on the roof. The stranger fuses the controls with a handheld sonic device and tells her that she needs to get out while he destroys the relay point. He warns her not to tell anyone what she's seen, as they won't believe her and it'll put their lives at risk. As Rose walks away from the store, there's an explosion from the top of the building. Everyone in the streets panic and Rose, still clutching the mannequin arm, runs home, going by an old-fashioned 1950s police box.
When Rose gets home, she finds Jackie watching the newscast about the explosion. Jackie isn't particularly upset about rose's condition and suggests she file a lawsuit for shock and emotional damage. Mickey comes over and tries to get Rose to go to the pub for a drink, but she figures he just wants to go there to watch the day's match on the big-screen TV. She sends him on his way and gives him the mannequin arm to throw away. He tosses it in the bin as he leaves, but it continues to rattle inside long after he's gone.
The next day, Rose wakes up at her usual time but doesn’t have a job to go to. As she has breakfast, she hears a noise from the cat flap. Investigating, she finds the Doctor peering in. He says his tracking device has led him there and suspiciously checks to see if she's made of plastic. Satisfied that she isn't, he prepares to leave but Rose drags him inside to ask him what's going on. Jackie notices the new attractive man and makes a pass at him but the Doctor doesn't seem to notice.
The Doctor looks around the sitting room while Rose makes coffee. He hears behind the sofa and goes to investigate, and the severed arm moves on its own, trying to strangle him. He throws it off just as Rose comes in and it attacks her. Using his sonic device, he renders it immobile with his sonic device. He prepares to leave with it but Rose demands answers. He explains that although the world at large isn't aware of it, he's struggling against an alien race that can control plastic with thought waves. He used his sonic screwdriver to cut off the signal to the arm, and now he needs to find its controller. As they go outside, Rose asks who he really is and the Doctor speaks poetically of how he is the one who knows of the world and can feel it rushing through space. He's surprised that Rose is interested but tells her she needs to go back to her ordinary life. She reluctantly leaves as he walks toward a police box. When she hears a grinding noise, she goes back only to find that he's disappeared.
Rose goes to Mickey to use his computer to do an online search. She finds one site with a photo of the Doctor, run by a man named Clive. Despite Mickey's warnings, Rose goes to Clive's house and Mickey drives her there. He stays out in the car while Rose meets with Clive, a seemingly normal man with a family. Clive invites her in to look at his research. As he waits, Mickey notices a plastic garbage bin seemingly moving on its own toward him. He opens it up but doesn’t find anything inside. However, his hands are stuck to the plastic, and the plastic starts to pull him in. Mickey falls inside and the bin gives out a large belch.
Rose goes into Clive's garden shed where he keeps his research. Clive has collected drawings and articles on the Doctor from throughout the last century. One photo shows the Doctor near the site of John F. Kennedy's assassination, and another has him stopping a family from going on the maiden voyage of the Titanic
. One drawing shows him on Sumatra just before the eruption of Krakatoa. Clive warns that there are dozens of legends of the mysterious Doctor, and in each one he brings death and destruction to everyone he meets. When Rose wonders who the Doctor could be, Clive suggests that he's an immortal alien who travels the Earth. Creeped out, Rose runs to the car where a smiling shiny Mickey greets her.
Rose and Mickey go to a restaurant for lunch and Rose wonders what job she's going to take now. Mickey starts asking her about the Doctor and how they met, and what the Doctor plans to do next. Rose isn't interested and doesn’t know, but Mickey persists... until the Doctor arrives, pretending to be a waiter. He fires cork from a champagne bottle into Mickey's forehead, revealing that he's a plastic replica. The replica attacks the Doctor, who grabs it and yanks its head off. The headless body goes after them and the Doctor and Rose run out the back door into the closed-off courtyard behind. The Doctor seals the door with his sonic screwdriver and goes into the police box, which is now in the courtyard. Rose follows him, but then backs out, shocked. The replica starts to hammer its way through the sealed door and Rose has no choice but to go inside the police box.
Inside the doors of the police box is a huge chamber with a central six-sided control panel. The Doctor is wiring the head into the control panel. Seeing Rose's shock expression, he says that the police box is a TARDIS, it travels through time and space, and he's an alien. Seeing the head, Rose believes that the real Mickey is dead. The Doctor, unconcerned, gets upset when the head starts to melt. He desperately tries to track the control signal and the TARDIS shakes. However, he notices that it's too late and goes outside. Rose follows him and discovers that they're now on the banks of the Thames.
The Doctor still is unconcerned about Mickey's death and informs Rose that the Nestene Consciousness is the invading alien force. He has a vial of "anti-plastic" he can use to destroy it, but has no idea where it is. It plans to field on Earth's toxic atmosphere after its own feeding planets were destroyed in a war. The Doctor explains that it needs a large wheel-shaped device to transmit its control signal to the mannequins and the replicas. As the Doctor mutters away, Rose notices the London Eye nearby and finally manages to get the Doctor to notice it. Happy she's been of help, the Doctor grabs her and they race across the bridge to the tourist attraction.
Rose finds an entrance to the service tunnels beneath and they descend to find a pit filled with living moving plastic: the Nestene Consciousness. The Doctor demands a parlay under galactic law, while Rose spots Mickey, alive and well and hiding in fear. The Doctor casually explains that he knew the Nestene kept Mickey alive to maintain the replica, but is unconcerned about Rose's anger toward him for not saying anything. He approaches the Nestene but two of its mannequins grab him and find the anti-plastic. They have also found the TARDIS, which the Nestene recognises as a high-technology device. The Doctor claims it's all a misunderstanding and the vial of anti-plastic was an insurance policy, nothing more. The Nestene doesn't believe him and identifies him as a "Time Lord." The Doctor says he tried to save them during the war but the Nestene sends a signal to activate its forces throughout London.
Rose tries to call her mother but she's too far underground to get a clear signal. Jackie is at the shopping centre, as is Clive and his wife and son. They look on in horror as the store window mannequins come to life and smash their way through the glass. One of them advances on Clive and the front of its hand swings open to reveal a blaster. It kills Clive, and his wife and son run outside along with Jackie. However, the Nestene-controlled mannequins are everywhere, killing whoever they find. Jackie tries to hide but three of the, dressed in bridal dresses, advance on her.
Rose and Mickey are trapped when the passageway out collapses due to the power of the activation signal. With the Doctor captive and Mickey immobilised with fear, Rose realises it's up to her. She cuts free a chain and swings into the mannequin holding the vial of anti-plastic. It drops it into the vat as it falls in and the anti-plastic flows into the Nestene. It screams in agony and fury and starts to break up. Everyone gets into the TARDIS and they hastily depart as the Nestene is destroyed. Outside, the mannequins go inert with the guiding intelligence eradicated.
The Doctor rematerialises the TARDIS in a nearby back alley. Mickey runs out and hides behind the garbage, cowering in fear. Rose calls her mother and make sure she's okay but quickly hangs up. The Doctor says that the Nestene are defeated, and admits that Rose saved the day. Impressed, he offers her the chance to travel with him. She considers it, but reluctantly decides to stay and help Mickey and Jackie recover. Saddened, the Doctor steps into the TARDIS and it dematerialises. However, as Rose turns to go it reappears and the Doctor pops out to add that it also travels in time. Given a second chance, Rose quickly kisses Mickey goodbye and leaps into the TARDIS.