The TARDIS gets caught in a time eddy. Despite the Doctor’s best efforts to break free the time machine continues to lurch and bounce. Suddenly they are joined by a newcomer who arrives unannounced in the control room. He is tall, good-looking and well dressed. He is haloed in golden light and immune to the movement of the ship. Donna demands to know who the man is and where he came from. The Doctor is under the console, oblivious to the presence of the newcomer, who starts to advertise ‘The Edifice’. He addresses Donna by name and tries to sell her some real estate. He produces a glossy brochure and talks about the luxurious features. The Doctor sees the man and tries to shoo him out, exasperated that he got through the TARDIS filters. He says the man is sentient spam mail, bio-calibrated to the recipient. The Doctor tries to use the controls to remove him but a sudden lurch of the TARDIS causes Donna to brush against the man’s hand and the brochure. He says, Congratulations,” to her and vanishes. The Doctor glares at her, asking her what she did.

The TARDIS suddenly settles down to travel smoothly. Donna has the sensation that she and the world around her are diminishing. The TARDIS lands inside something unrecognizable. Outside the door stands a featureless barrier. Donna states that it is plywood. The Doctor disagrees and takes out his screwdriver. He declares it to be an immovable inert barrier until Donna pushes it aside. They see a rather pleasant bedroom. The TARDIS is in a walk-in wardrobe with plywood backing.

Puzzled, the Doctor looks around the room, wondering where they are. Donna is delighted by the furnishing in the lounge, declaring it ‘tasteful’ in a husky voice. She says it is like a show home. The Doctor looks at a welcome-basket of fruit and extracts the card. Donna calls him over to look at the view from the window. White mountains, standing impossibly high, and a sky holding a golden sun entrance her. She says she has never seen anything like it but the Doctor draws her attention to what lies below them; Chiswick. He opens the window and touches something outside, causing the view (sky, mountains and Chiswick) to ripple.

He says the building is feeding on their memories to make them feel at home. Chiswick is her home, the mountains are Gallifrey. Donna is astonished at how beautiful his home was. She wants to know why the apartment wants them to feel at home. He tells them that they are at home. He shows her the card which welcomes them to apartment 16064 on an Edifice Life-hold Lease. He says that she accidentally signed something in the TARDIS and leaving won’t be easy.

The Doctor tries to get the TARDIS to work, but the dematerialization circuit is jammed. He speculates that it is part of the contract that Donna signed. She insists that she didn’t sign anything but he tells her that touching the brochure was probably a binding agreement. It would have triggered a massively powerful matter transfer device that pulled them into The Edifice. She says that this is kidnap, but the Doctor is already wondering how many other people this has happened to. Donna walks back over to the window. There is a knock at the door. She peeps through the spy-hole into the corridor and sees someone small. She opens the door and sees a little old lady, the size of a child, with antennae that give away her less than human origins. She says she is a neighbor and has come to welcome them. She holds out a fruit cake and walks into the apartment. Donna introduces herself and the old lady, Edie, admires the view. She says that she has been a resident for a week. She says she loves the apartment she has, though she can’t actually remember signing an agreement to live there. She finds it odd when the Doctor asks her where the exit is, asking why anybody would want to leave. She tells them that if there are any problems they should use a button to call ‘the super’, but she has no idea where the button is. There is a noise in the corridor, a heavy shuffling. When the Doctor goes to the door to investigate, Edie rushes to his side and tells him not to, pushing the door closed. The shuffling continues, accompanied by a growl.

She tells him it is Mister Gnur, not an ideal neighbor. The Doctor peers out of the spy-hole. When Donna tries to look out, too, the Doctor warns her not to. Talons scratch at the door. Edie says that he eats other residents. After the monster has gone, the Doctor takes Edie home. They wander down the hallway to investigate. Donna asks who the building’s owners might be. The Doctor says that is what he is trying to find out. The hallway stretches on in front of them, curving away slightly. The Doctor says he thinks the building has been ‘warped’, folded in on itself like an Escher painting. She asks if they keep on going will they meet themselves. He says no, because that would be embarrassing. They find a stairwell behind a door.

The warped geometry is more obvious on the stairs, which seem to extend both up and down in front and behind her. Donna feels sick as she tries to make her way down, feeling as if she would fall sideways at any second. The Doctor is enjoying himself and tells her she cannot fall because there is no down or up. He calibrates his screwdriver and holds it to her ear. This decreases her alarm. He says she is merely feeling ‘floopy’. They carry on down the stairs. The Doctor stops on a landing and peers at the wall. There is a brown stain, spreading downwards, getting darker and thicker the further it stretches. Donna asks what it is. The Doctor touches it, and then licks the tips of his fingers. Grimacing, he says it is familiar, but he isn’t sure what it reminds him of. He says it is spreading from below. They hear someone coming up from below, whistling. He is a tall man in fluorescent clothes, walking a rat-like creature on a lead. The man greets them and introduces them to his pet, Zuzu.

The man says he leaves on floor 165. He tells them that he has heard the floors are full past 175, but above that the floors seem to stretch on forever. The Doctor asks if the man has seen the super. The answer is in the negative. The man leaves them, warning them to avoid floor 139 because of a’ bad element’ down there.

They descend a few more floors. Every now and then they hear noises: cries, laughter and singing.=2 0Below them they see lights ascending. Soft footsteps approach. A party of figures in ragged clothes advances towards them, carrying flaming torches.. They are a mixed crowd of aliens, all dressed in ragged clothes, all of them showing fear on their faces. When they see the Doctor they tell him they are refugees, fleeing the depths. They say it is hell below, and they are escaping the warzones. They list bad neighbours, including Rutans and Sontarans. The refugees say they climb everyday to find safety but there is always danger and death ahead of them. They were two-hundred strong when they set out, and have been travelling for two years. Now there are only twenty of them and they only trust each other because everything else they meet tries to kill them. They begin to move threateningly towards the Doctor and Donna.

They produce primitive weapons and rush forwards. The Doctor bursts through a door marked L141 and uses his sonic screwdriver to lock it behind them. He says none of the races they have just encountered was born to be killers, unlike the likes of Rutans and Sontarans. The building has been sucking in victims indiscriminately. They look around at floor 141. It is similar to 160 but has fared less well; there are scorches on the carpet, l ights have been shot out and blood on the walls. They advance past half-open doors where they hear sobbing and praying. Distant noises sound like gunfire. The smell of rotting fish permeates the air. They hear a whirring and a ping. Ahead of them a pair of doors opens and they see a lift. An antlered female steps out of the lift, and then steps back in, announcing it is the wrong floor. The Doctor runs up to the lift, arriving just too late to stop the doors closing. The lift departs. Donna notes that there is no button to summon the lift.

An argument breaks out in a nearby apartment so they move on. The smell is getting worse, coming from an open apartment. They step through the door. Inside there are three squid-like creatures. The Doctor says they must have died the moment they arrived, killed by the air and the pressure differentials. Five figures step up to the doorway behind them. They are a small robot, two tall mollusks, a woman with wood-bark skin and their leader, a man in a Hawaiian shirt, Bermuda shorts and sandals. He tells them to come out, training a gun on them. The man demands to know who they are, introducing himself and his companions as the level 141 residents association. The Doctor finds this concept brilliant. When they say they come from 160 the man wonders why they have come down. He says that everyday more murderers and thieves arrive.

The Doctor reassures them that he is not a murderer or a thief. The man with the gun asks him to explain the deaths of Mister and Missus Krill and their son Philip, indicating the dead squid. The Doctor begins to explain that they were dead when he arrived, but is taken aback by the fact that they had names. The residents’ representatives hold out a card from the Edifice, asking them to welcome the Krills. They then say that they have drawn up a charter to use ultimate sanctions against anyone who threatens the safety of residents from floor 141. The Doctor is effusively delighted that people can make up and live by their own rules in such adverse circumstances. Donna points out that these rules mean that the representatives of the residents’ association are going to shoot them. Just as the man with the gun is about to pull the trigger a blue flame cuts a circle out of the carpet behind them. The circle of floor falls away and a ladder appears in the gap. Warriors in silver armour and plumed helmets climb up. The first one warrior shoots at the residents with a gun that spits hypersonic needles. The robot explodes and the woman with wood-bark skin dies quietly. Six other warriors step20up and kill the other residents. The Doctor and Donna escape up the corridor as the warriors erect a holographic flag before kicking open apartment doors and murdering the people inside.

The Doctor and Donna climb out of the window of their apartment onto a metal ledge. They step through the projected image of the view. Looking back they see The Edifice, stretching away in every direction. They are standing outside a metal world, encased in a black superstructure of girders. Beyond the girders they see the blackness of space and a field of stars. Behind them one of the silver warriors reaches through the window of the apartment and stretches its hand beyond the projected view, groping its way towards them.

They edge away from the hand which pulls back in through the window. Donna can’t breathe but the Doctor says they are still inside the Edifice’s atmosphere. She gasps that she is having a panic attack so he gives her a paper bag to breathe into. They gaze out into infinity. When she r eturns the bag she remarks that it smells of jelly babies. They peer down at the levels below but the expression on Donna’s face tells him they won’t be shimmying down. They climb back into the Krill’s apartment and creep to the door. In the distance they hear muffled gunfire. He says that the silver warriors are members of the Karturan Empire and are natural conquerors. They will have spread out in both directions and will be murdering occupants apartment by apartment. He studies their holographic flag in the hallway. Off to their left they hear more gunfire so they go to the hole in the floor and lower themselves down the ladders. On the floor below all seems quiet.

Level 140 is as damaged as the floor above. They feel a breeze from up ahead and follow the corridor. The walls and carpets are in worse condition here; stains like those on the stairs are eating the structure away. A door frame collapses. The stains have eaten away the floor, making holes into the floor below. There is a tearing crash and the Doctor falls through the floor. He hangs onto the edge of the hole which crumbles around him. Donna tries to reach him but he warns her away. Ignoring him she leans down but he keeps slithering away. She asks for him to throw her something, such as a scarf but he replies he has no scarf. The lip of the hole crumbles away and the Doctor vanishes. She scurries away from the edge. She shouts down to him but there is no reply. She runs back to the hole and pills all the ladders down, then selects the most robust and drags it back to the rotten hole. She slides it over the edge into the darkness below. She begins to climb down as fast as she can. The hole above collapses again and the ladder falls. Fortunately, she only has six inches to drop to the floor.

She hisses the Doctor’s name. Her eyes adjust to the gloom and she sees that on this level there are no doors, walls or carpets. The floor is slimy and the sounds of scratching can be heard. The Doctor reaches out to her and scares her. He checks them both with his sonic screwdriver. He asks her what floor they are on. She replies that they are on 139 and he reminds her that the man with the ratty pet told them to avoid the bad element on 139. He says he recognizes the slimy material that has made the stain: digestive enzymes. He leads her through the gloom towards a huge lump and says it is a Nanovore hive. Nanovore are colonial microbots that leak enzymes into the en vironment around them and then come out and eat everything. He says they probably ate the whole of the level around them. Their only protection is the sonic screwdriver which will keep the Nanovores away for a while until they adjust to the frequency. As they make their way away from the hive they see that Donna’s ladders have already been eaten. Finding a stairway they see that the stairs have been eaten too. They decide to follow the outer walls.

The hive is becoming more active and the Doctor suggests that they run. Some of the internal systems have been exposed by the enzymes. Periodically the Doctor checks if any of the wiring is intact enough for him to access with his screwdriver. A tide of Nanovores spreads across to the floor towards them. Just as it reaches their feet he aims his screwdriver and a whirring noise grows louder. There is a single ping and a lift door opens. They leap into the lift, but they both have Nanovores on their feet and lower legs. The Doctor uses the screwdriver to drive them off while the lift attendant closes the doors. He is a short man in a bellboy’s uniform. He asks them which floor they want. The Doctor just asks for any floor that isn’t 139. The attendant asks if they are hav ing problems with the neighbours. Donna asks the attendant who he works for. The Doctor tells her not to be so aggressive but the attendant replies that he doesn’t work for anyone. He says his name is Frank. He tells them that he doesn’t know who owns the Edifice and has never met anybody apart from residents. He replied to a job advert and immediately found himself doing the job. He says the person they need to talk to is the Super but he has no idea how to call him. He says he has the next best thing and turns a key which halts the elevator.

He uses the key to unlock a telephone and asks for the Super. After a while the Super appears in the lift. It is the same man as the salesman who appeared in the TARDIS. He asks what their problem is. The Doctor tells them that the Edifice is the problem. He demands to speak to whoever is in charge. The Super replies that he cannot help. The Doctor explains that millions of residents are dying but the Super says that management does not interact with residents (who are not allowed access to management levels). Then he vanishes.

Donna is scathing of the Doctor’s inability to get any information from the Super, but the Doctor replies that at least he has found out that management levels exist. Frank, the lift attendant, says he doesn’t know where management levels are. The Doctor asks to be taken to the core of the Edifice. They arrive somewhere near the centre of the structure but Frank can’t get them into the levels. His key, he says, does not have the priority to turn the last few notches. After some persuasion from Donna Frank lets the Doctor take over. He uses his screwdriver to get them where he wants to be. They step out onto the management level. Here, the ceilings are higher and everything is painted red. The elevator departs with a whir. There is a constant hum of machinery. The Doctor surveys it, saying it is just a fraction of the machinery needed to make the Edifice exist. They follow a gantry over a giant ravine filled with machinery. Arriving at a hatch they are confronted by an apparition of the Super who looks around and then vanishes. He may have been looking out for the interlopers or he may have been carrying out a planned inspection. They cross a further four ravines full of machinery. Donna is just complaining about how far they have walked when the Super appears again, beneath their level. This convinces the Doctor that they are being looked for and he starts to search for an information conduit. The Doctor sniffs and says he smell psionics, it smells like candy floss. He wonders where the source is. When another Super arrives near them they hide again. Donna asks what will happen if the Super catches them. The Donna tells her she is brilliant; the supers will whisk them away somewhere. He immediately makes a lot of noise to attract some attention. Three supers appear.

They find themselves on a platform that runs round an enormous drum-shaped chamber. It is oppressively wall. The walls are banked with lights and controls, including holographic screens. The centre of the chamber contains a tank of murky water, eight metres tall. It smells of candy-floss. The Doctor says it is the psionic residue of the Ilk. The Doctor tells Donna that they are a very old race of beings, difficult to communicate with, that feeds on emotions. This one has commandeered the whole of the control system for its own ends. The Ilk consume emotions psionically, the stronger the better. It has brought them to it to find out who they are and why they are meddling in its activities. He reaches out to touch a button but a loud voice in their head shouts, “Touch not.” The Doctor looks down on the Ilk, telling it that it has20put on a lot of weight feeding on the Edifice. It has built the tank just to support its bulk. He tells the creature that it has put on too much weight for its own good and he is going to cut it off from its food supply.

He starts to alter control pattern settings. There is a stench of candy-floss and the Doctor drops to one knee. He manages to push three more buttons before being knocked down again. Donna tries to help but the Doctor warns her away. He says he must save all the people in the Edifice. The support tank has blunted the Ilk’s psionic range and the Doctor scrabbles around on the control panel, altering settings. The fluid in the tank gurgles and froths, pouring away. The Ilk begins to emerge. The Doctor says he has to finish the settings before it can get out of the bath and use the full force of its psionic abilities. He thinks that the Edifice was a legitimate luxury development until the Ilk changed the salesman to a kidnapper to pull in more and more murderous races to fight each other. The despair and misery caused by this is the Ilk’s nourishment.

The tank finally drains, revealing a pale and wrinkled mass of blubber. Glistening limbs flail. Scores of eyes of all sizes blink open. Donna is not as afraid as she would have expected. Instead she launches a verbal assault, demanding to know how the Ilk dares to behave in this way. She goes on to ask if it has been feeding on her. The Ilk makes a grumbling sound as she goes on with her merciless tirade. Donna tells her not to make it angry. Another psionic wave drops the Doctor to his knees. Donna tells it to leave him alone. The Ilk recoils from her, making unpleasant noises. Then it crashes into the stanchion supporting the platform. Its tendrils reach for her, pulling off her shoe, grasping her legs. The Doctor reaches for her and pulls her to safety. She asks why he isn’t pushing buttons and he tells her he has pushed them all.

The Ilk vanishes. The Doctor says he has sent it somewhere far away and lonely. He tells her he succeeded because Donna was giving the creature indigestion. She choked it with the indigestible emotion of disgust which bought the Doctor time to finish his plan.