As the Doctor and Rose head for the station’s main reception area, a computer voice announces the arrival of further shuttles and reminds guests that weapons, teleportation, and religion are forbidden aboard Platform One. The rich and the elite of the galaxy are on their way to witness the death of the Earth; until now, the planet had been protected by the National Trust, which used gravity satellites to hold back the sun’s expansion and put the continents back in their classic positions, but now the Trust’s money has run out and nature is taking its course. The human race has evacuated, and within half an hour, the Earth will be destroyed.

As it begins to sink in for Rose that she’s about to witness the death of her home planet, a steward with bright blue skin arrives and is startled to see intruders in the hospitality zone. However, the Doctor presents the Steward with a psychically imprinted blank sheet of paper and manages to convince him that it’s an invitation. Rose, somewhat thrown by the Steward’s alien appearance, is taken even further aback as more alien guests arrive in the hospitality chamber: Jabe, Lute, and Coffa, walking humanoid trees from the forests of Cheem; the squat blue Moxx of Balhoon; the dark-hooded Adherents of the Repeated Meme; the brothers Hop Pyleen; Cal Sparkplug; the birdlike Mr and Mrs Pacoon; the sponsor of this event, a giant head in a jar known as the Face of Boe; and the Ambassadors from the City-State of Binding Light. The visitors exchange gifts to symbolise peace; Jabe presents the Doctor with a cutting from her grandfather, and the Moxx of Balhoon spits at Rose, offering the gift of bodily saliva. The Adherents hand out small metal spheres to the other guests, including the Steward, who tries to explain that he’s not actually a guest but finally takes the sphere to be diplomatic. The Doctor offers the gift of air from his lungs by breathing on the other visitors, and Rose notes uneasily that he and Jabe seem to be flirting.

The final guest is the Lady Cassandra O’Brien, the Last Human, who has just completed another round of plastic surgery to make her appear young and thin. In fact, she’s had so much plastic surgery that she’s now just a translucent sheet of skin with eyes and a mouth, stretched out tightly over a frame above a brain in a jar and constantly attended by masked surgeons who moisturise her skin to keep her from drying out. Cassandra offers gifts from Earth: the egg of an ostrich, an extinct animal believed to be a fire-breather with a 50-foot wingspan; and a 1950s jukebox which she mis-identifies as an iPod. The alien guests begin to mingle as the jukebox plays Soft Cell’s Tainted Love, and Rose, overwhelmed, finally succumbs to culture shock and rushes out of the hospitality zone. Jabe takes a quick scan of the Doctor as he follows Rose out, but it takes the scanner quite a while to identify his species -- and when it finally does, Jabe is astounded. Nobody notices when one of the silver spheres handed out by the Adherents opens up and a small robot spider scampers out...

Rose finds her way to a small side room, but as she watches the expanding sun through the window, a small blue woman in a maintenance worker’s uniform arrives. The woman remains uncomfortably silent when Rose addresses her, and eventually explains that Rose must give her permission to speak. She is surprised and delighted when Rose does so, and sets to work on a nearby maintenance hatch, explaining that she’s just popped in to repair a minor glitch in the plumbing of the Face of Boe’s suite. Rose asks the woman, Raffalo, where she’s from, and Raffalo explains that she’s from Crespallion -- which isn’t a planet, but part of the Jaggit Brocade, affiliated to the Scarlet Junction, Convex 56. Rose has no idea what this means, and it finally sinks in with her that she’s left behind everything familiar in her life to travel with a complete stranger through worlds she knows nothing about. Rose bids goodbye to Raffalo and retreats to a private viewing gallery to think about what she’s done. Once alone, Raffalo removes the hatch and crawls into the service ducts, where she’s surprised to encounter the small robot spider. At first she thinks it’s an upgraded maintenance robot, at least until it’s joined by several others. Raffalo realises too late that she might be in trouble, and the spiders drag her, screaming, into the ductwork...

Back in his office, the Steward receives a call from the computer Control informing him of the unidentified blue box in gallery 15; irritated, he makes a public announcement requesting that its owner report in and reminding guests that teleportation aboard the station is forbidden under peace treaty 5.4/Cup/16. The attendants remove the TARDIS from the viewing gallery and give the Doctor a ticket so he can reclaim it once the event is over. Meanwhile, more robot spiders are emerging from the silver spheres and scuttling through the station’s service ducts...

Rose sits alone in a viewing gallery and catches herself actually trying to strike up a conversation with the cutting from Jabe’s grandfather. She fails to notice the robot spider crawling out of the silver sphere behind her; for some reason, it seems to take an interest in Rose, but it darts off without being noticed when the Doctor enters to check up on his companion. Rose admits that she’s having trouble dealing with so many aliens, but when she asks the Doctor where he’s from, he evades the question. When she asks why the aliens are all speaking English, he explains that the TARDIS is generating a telepathic field within her brain, and is surprised by her reaction when she realises that her perceptions have been altered without her knowledge or permission. Frustrated, she presses him for an answer to her first question, demanding to know who he is and where he’s from, but he loses his temper and refuses to speak to her.

Realising that she won’t get any more out of the Doctor, Rose tries to make the best of it; after all, he’s her only ride home, as she demonstrates by pulling out her cell phone and noting the lack of signal. The Doctor, now calmer, takes her cell phone and sticks a technical doohickey in the back slot -- and, to Rose’s surprise, she finds that she can now use the cell phone to call up her mother. She seems to have reached Jackie before the Nestene attack, as Jackie asks Rose to put some money in the store’s lottery syndicate for her. Jackie is somewhat surprised that Rose is calling in the middle of the day, but Rose assures her mother that she’s just fine. This small slice of normality has helped Rose cope a little, but as she hangs up, it occurs to her that her mother has been dead for five billion years. As this starts to sink in, however, the entire station shudders -- and the Doctor realises that something’s gone wrong...

The Steward publicly announces that the mild turbulence was caused by a gravity pocket -- but privately, he’s scrambling to find out what just happened. When he scans the infrastructure of the station, he’s startled to detect the robot spiders crawling through the ducts -- but he’s even more startled when one of the spiders scuttles into his office and operates the controls, lowering the sun filter over the window. The Steward is unable to raise the filter again, and the room fills with the blazing, unfiltered light and 4,000-degree heat of the sun...

The Doctor isn’t fooled by the Steward’s attempt to keep his guests calm, and he shares his concerns with Jabe. She offers to show the Doctor to the maintenance hatch behind her suite so he can investigate, but isn’t sure whether to address Rose as the Doctor’s wife, partner, concubine, or prostitute. Irritated, Rose sends the Doctor and Jabe on their way while she stays to chat with Cassandra, the only other human in the room; however, it turns out that they have little in common. Rose listens politely as Cassandra reminisces over her youth as a little boy growing up in the Los Angeles Crevasse, but when Rose asks about the rest of humanity, Cassandra dismisses them as mere mongrels; she’s the last pure human left. When Cassandra advises Rose to consider some plastic surgery of her own, the disgusted Rose announces that she’s got more right to call herself “the last human” than Cassandra, who’s had everything human about her nipped and tucked away until all that’s left is skin and lipstick. Rose storms out, leaving the rather ticked-off Cassandra behind -- but the Adherents of the Repeated Meme follow Rose into the corridor, knock her unconscious and drag her away...

On their way to the main computer complex, Jabe explains that she’s here partly to be seen and to make connections with the other visitors, but mainly to show respect for the Earth, her ancestral home; Jabe herself is a direct descendant of the Earth’s tropical rainforest. She also explains that Platform One is controlled by a top-of-the-line computer mainframe, and that the guests have been assured that nothing can go wrong -- but the Doctor has had experience with “unsinkable” ships before. And if they really are in trouble, there’s nobody around to help them. Jabe notes that the Doctor seems a little too excited by this, and as he tries to break into the computer complex with his sonic screwdriver, she wonders what kind of person enjoys seeking out trouble; perhaps someone who has nothing else left... Jabe admits that she knows who and what the Doctor is -- and that she understands just how much he’s lost. The Doctor, struggling to hold back his emotions, opens up the door to the computer complex, where gigantic fan blades sweep across a maintenance catwalk, cooling down the computer’s central processor. When the Doctor opens up an access panel, one of the spiders scuttles out. Jabe catches it with her liana, and when she and the Doctor examine it, they conclude that it’s been committing sabotage. And with the Earth due to explode in ten minutes, the people aboard Platform One might be in a great deal of trouble...

Back in the hospitality suite, the guests continue to mingle as the jukebox ushers in Earth’s last minute with a traditional human ballad: Toxic by Britney Spears. Meanwhile, the Doctor and Jabe visit the Steward’s office, only to find that he’s been killed -- and when the Doctor tries to repair the damage, he learns that another sun filter has been programmed to descend elsewhere on the station. The Doctor investigates, and finds that Rose has been locked inside the gallery in question. As the filter begins to descend, the Doctor struggles to reprogram the computer while Rose keeps as close to the floor as she can. Fortunately, the Doctor is able to reverse the damage and raise the filter again, but the top half of the room has been scorched by the searing heat, and the door lock has melted. Rose has no choice but to stay where she is while the Doctor sets off to confront the villain responsible.

Jabe reports to the other visitors that the spiders have somehow infiltrated the entire station and killed the Steward. Cassandra accuses the Face of Boe of setting them all up, but the Doctor reveals that he’s reprogrammed the spider he and Jabe caught to return to its controller. The spider scuttles towards Cassandra, and then veers away towards the Adherents of the Repeated Meme; the guests had all accepted the Adherents’ silver spheres as gifts, and thus carried them past the code locks, spreading them throughout Platform One. But the Doctor reveals that the Adherents are remote-controlled androids, and after some prompting, the spider returns to Cassandra, the last human (which may be why the spiders seemed attuned to the human Rose earlier). Cassandra’s surgeons hold off the others with moisturisers filled with acid, and Cassandra admits that she intended to manufacture a hostage situation in order to sue the owners of Platform One for compensation; however, as she has now been exposed, she intends to fall back on her secondary plan. She has shares in the other visitors’ rival companies, and when they are killed, those shares will triple in value -- and Cassandra will spend her fortune on more plastic surgery, ensuring that she, and not Rose, remains the last pure human in the Universe. Cassandra now remote-detonates all of her spider drones. The explosions rip through the mainframe, taking out computer control and shutting down the station’s force fields. Cassandra and her surgeons then teleport out, leaving the others, who had complied with the restrictions against teleportation, stuck on Platform One.

Convinced that there must be a manual reset switch, the Doctor takes Jabe back to the computer complex. Unfortunately, the reset switch is on the other side of the catwalk, and as the heat rises, the fans speed up. The lever controlling the fans refuses to stay down on its own, and despite the Doctor’s protests, Jabe remains to hold it down, telling the Doctor to stop wasting time -- after all, he is a Time Lord. The Doctor makes a hazardous dash forward through the rotating fan blades, but the heat is quickly rising. The exo-glass in the station’s viewing panels begins to crack and shatter, and spears of intense light cut through the reception hall and the viewing gallery where Rose is trapped. The Doctor has only made it past two of the three fans when Jabe bursts into flame and lets go of the lever; however, with only ten seconds to go before the end of the world, the Doctor calms himself down, closes his eyes, and steps forward -- passing safely between the blades. He then pulls the reset switch and orders the computer to reactivate the shields, and it does so just as the Earth is struck by the outer atmosphere of the sun and explodes. As the station’s internal temperature returns to normal, the fans slow down, and the Doctor walks back down the catwalk to stare grimly at what remains of Jabe.

Rose makes her way to the reception hall, where she finds that the Moxx of Balhoon, amongst others, has been reduced to ashes. The Doctor returns alone, and after telling the stricken Lute and Coffa what’s happened to Jabe, he angrily picks up Cassandra’s “ostrich egg” and smashes it open, revealing the teleportation feed she used to beam herself through the 5,000-degree heat outside Platform One. When the Doctor reverses the feed, Cassandra materialises back in the reception hall. Initially shaken, she recovers her poise and challenges the Doctor to try charging her with murder; determining whether aliens legally count as “people” will keep the courts tied up for years. But the Doctor then points out that he’s transported her back without her surgeons, and her skin is drying out rapidly in the hot, dry air. Even Rose takes pity as Cassandra begs the Doctor to save her, but he refuses; everything dies eventually, and the last human has had her time. With a last agonised cry (“I’m too young!!”), Cassandra’s skin dries out, stretches, and splits, splattering the last human across the reception hall.

Later, as the survivors depart and the computer shuts down for maintenance, the Doctor finds Rose watching the Earth’s remains float past the viewing window. In the final moments, everyone was too busy trying to save themselves to look outside, and when the Earth’s long history came to an end, nobody was watching. The Doctor leads Rose back to the TARDIS and takes her back to 21st-century London, where she sees people walking down the street, living their ordinary lives and taking it all for granted -- something Rose will never do again. The Doctor finally admits that his home planet was destroyed in a war; he is the last of his people, the Time Lords, and he travels alone because he has no one else to share his travels with. Now he’s shown Rose just how dangerous those travels can be. After a moment, Rose makes her choice: she’ll keep travelling with the Doctor, but first she wants some chips. She’s still got the opportunity, as the shops won’t close for another five billion years.