In a frozen forest landscape animals are fleeing in terror from some nameless evil. A female saber-toothed tiger is desperately hunting for food for her cubs.
The Doctor is homing in on a planet intent on saving the inhabitants from the Voracious Craw, one of a race of creatures that are the size of a space ship and that hover across the surface of worlds devouring everything. They resemble inflated tapeworms. On the scanner Martha can see a pale green frozen world called Tiermann’s World. The Craw can be seen thirty-six hours away from the planet’s only settlement. The Draw has a debilitating effect on technology and even the TARDIS is unhappy about being so close.
Stepping out of the TARDIS they are confronted by the female tiger. Just as it is set to spring onto them a teenage boy, carrying bags of sophisticated camera equipment, steps into the space between them. Martha flings the boy to the floor while the Doctor runs whooping into the distance to distract the tiger into pursuit. When next Martha sees the Doctor he is talking quietly to the tiger, persuading it to return to its young and to look after them. The tiger pads away.
The boy introduces himself as Solin and says he is one of only three people on the planet. They live in the Dreamhome which provides all that they need and he cannot understand why the Doctor has said he has come to rescue them. His father already knows that danger is approaching and the three of them are preparing to leave on their rocket.
The trio make their way through the woods to the Dreamhome. Solin explains that he was born on the rocket trip to this world and has known no other home (nor any other people apart from his parents).Solin’s father was once a gifted scientist who bought the planet with his money from the Servo-furnishing industry. On their way their progress is blocked by a shimmering force field beyond which is a pale yellow mansion house. Solin opens a panel in a bright red pillar box and enters a code which opens a doorway for them through the force field.
The air inside the shield is warm and balmy but Martha barely has time to voice her appreciation when the force field begins to break down. At first Solin blames himself for breaking it but the Doctor tells him it is more likely to be the effects of the approaching Voracious Craw.
The Doctor is attempting to fix things when a lawn mower and a water cooler race across the lawn to finish the repair. The Doctor and Martha liken them to 1950s sci-fi visions of what future robots would look like as Solin tells them that nearly everything in the house is a robot.
They make their way to the house where they are met by Professor Ernest Tiermann. The Doctor repeats his warning of the inevitable danger that is approaching and Tiermann leads them inside to see his luxurious and tasteful home. They are served sherry by a robot drinks cabinet called Walter. When the Doctor asks the professor about his plans he is told that the three humans are set to leave in a rocket but the robots will be left behind. When the Doctor suggests that this lacks compassion Tiermann makes it clear that he only thinks of his robots as toys.
Tiermann insists on giving them luxurious rooms with adjoining doors. They prepare themselves for dinner, Martha in the bath and the Doctor by mulling over Tiermann’s chilly, almost creepy, nature. After her bath Martha finds that a robot seamstress has rustled up a pale cream gown for her to wear at dinner. The Doctor moans about his lack of new suit, but is more outraged by the fact that the Tiermann family do nothing for themselves, letting the robots do everything for them. Martha is more concerned that the TARDIS is out in the frozen wilderness and the Doctor has done nothing to retrieve it.
Tiermann spends most of his time before dinner pacing about and holding forth on a variety of topics while his wife Amanda, sits quietly, beautiful and demure. Tiermann brags in particular about the ship he designed himself and which will soon be taking them to Station Antelope Slash Nitelite. The Doctor accuses Tiermann of delaying his departure too long. The scientist replies that he does not like panic and came to this world to avoid such niggles.
Martha can barely concentrate on her dinner. Partly this is because of the tension building up between Tiermann and the Doctor and partly because of the robot sitting next to Amanda which swoops in and consumes her food every time she raises it to her lips. As the argument grows more intense Solin and Martha step onto the veranda for some cool air. Solin says that his mother only ever eats in private. He then declares himself attracted to Martha and wishes to kiss her. When she rebuffs him he marches off, chagrined.
The Doctor stays up after the rest retire for the night. He asks a robot, Stirpeek, to leave the doors onto the veranda open in case he goes for a run around the garden. The robot is suspicious but acquiesces. The Doctor races across the lawn to the force field with the intention of getting back to the TARDIS, about which he is actually very worried. He has barely opened a doorway in the shield when Stirpeek arrives to stop him, shooting a laser at the Doctor’s hand and warning him that the robots are all authorized to kill anyone who threatens the security of the Dreamhome.
He is led back to the drawing room where everyone is waiting for him. Tiermann accuses him of sabotage, but the Doctor is more concerned about the TARDIS. However, Stirpeek announces an 84 per cent failure in the force field. The Doctor insists that this is due to the approach of the Voracious Craw but Tiermann has him put into the cellars. The robots take him to Level Minus Thirty Nine where all the useless junk is taken.
In the night Martha tries to get to the elevator to rescue the Doctor but it refuses to respond to her requests and she is guided back to bed by Stirpeek. When she dresses in her old clothes and makes her way to breakfast it is already well into the morning and the house is a flurry of activity as the family at last begin preparing for departure.
The parents ignore Martha but Solin sits in the kitchen with her while she drinks coffee. Amanda has told him he can only take a few things due to weight restrictions and he is worried that Martha will be left behind. His mother reassures him but no mention is made of the Doctor. They can see Tiermann in the garden sloshing petrol onto the lawn with his robots methodically copying him. He lights a ring of fire around the house to compensate for the malfunctioning shields.
A tablet robot tries to give Solin some nerve pills but he refuses. The robot becomes more insistent and he tells Martha it has gone haywire, probably due to the approach of the Craw. They end up running away to the drawing room where Martha demands to be taken to the Doctor. Solin says he cannot do this. Instead they look at the view screens which show Martha the valley that they are in, as large as an Earth continent, and on the other side of the mountains is the Craw, sucking up matter like a huge tornado into its gaping mouth.
On level Minus Thirty Nine the Doctor makes friends with two robots, a vending machine called Barbara and a sun bed called Toaster. Both have been told of the Voracious Craw by the Dreamhome itself, which (they report) is not happy about events. The Doctor makes some repairs to Toaster which give it a new lease of life.
Tiermann tells Martha that the punishment for the Doctor’s perceived sabotage is that he is to be left behind to meet his demise. Martha argues that all the malfunctions are the result of the Craw’s proximity but Tiermann will not listen, even when three more robots behave erratically in the kitchen. Their argument is interrupted when a horned bear bursts through the wall of flames onto the lawn.
Barbara leads the Doctor to a secret exit which will take him down to Level Minus Forty. This is the home of the Domovoi, the spirit, heart and intelligence of the Dreamhome. She is Tiermann’s finest creation. Because she is hardwired to the Dreamhome she cannot leave when the family does, and she is not happy about it. Advancing down a torch-lit corridor they pass through wrought iron doors into a sanctum containing a magnificent fireplace. This is the Domovoi. She is mournful, and not a little unbalanced. When the Doctor says he will try to save all the robots, including her, if she helps him get back to his ship, she agrees, but hints that she has other plans of her own.
The horned bear crashes through a window into the house and destroys three robots. Tiermann flees in panic., seals off that part of the house and then reverts to his old bravado. On a screen they see the Doctor and two robots emerging from the lift, right into the path of the bear.
The Doctor escapes by getting Barbara to get in touch with the kitchen robots, setting them to thawing and cooking all the meat in the Dreamhome. As a diversion while this is happening he gets Barbara and Toaster to delve into their memory banks and the three of them sing ‘Bohemian Rhapsody’. When the meat is ready and the bear is feeding the Doctor sets off to confront Tiermann. He tells the scientist that he has met the Domovoi, which angers the scientist and (Martha detects) makes him a little fearful. The Doctor informs Martha that the Domovoi is a super computer, apparently made out of green fire. At that moment the screen in the drawing room changes to show them the Domovoi itself. She calls Tiermann a snivelling worm and then insists she is going to protect them all, as is her duty, by locking them inside the Dreamhome. After a maniacal laugh the screen goes dark.
While the Tiermann family is in despair the Doctor is determined to rescue everyone. Walter, the drinks robot, attacks the scientist with bottles and while Martha tends to his wounds Toaster destroys Walter with a bolt of blue lightning. Barbara is distraught at robot killing robot and the Doctor is worried that she may be taken over by the Domovoi. Tiermann’s injuries are not too serious, mainly because he has replaced many of his organs with plastic and metal. Suddenly the floor opens up beneath them and they fall deeper into the house. They land softly in a room full of fabrics. Martha suggests that Tiermann must have built an over-ride into the Dreamhome computer and the scientist agrees. There is a room that even the Domovoi is ignorant of where they can detach her consciousness. Just as the Doctor demands to be taken there the Domovoi speaks from the screen denying that such a room exists. The Doctor uses his sonic screwdriver to let them out into the corridor, where they find that they are on Level Minus Six. Just then they notice it is getting very hot.
The floor beneath their feet is melting. Tiermann finds an escape hatch just as his wife passes out. Making their way along a service corridor they hear the Domovoi looking for them, her voice sounding more deranged. They make their way down a stairway to Level Minus Twenty, but they are met by flying robots, tiny Sukkaz – flying vacuum cleaners – each with red malevolent eyes. As the party run to escape Amanda is snatched from Barbara, who was carrying her, as is Solin who goes to her rescue. They are lifted away up the stairs. Tiermann says they will be taken to The Dust Chamber, a vast hall filled with all the dust they have collected. The Doctor, Martha, Tiermann and the two robots press on towards the override room.
The override room is small and inconspicuous with an insignificant-looking panel of controls. Before Tiermann can press the last button Barbara is possessed by the Domovoi, shrieking that they will all die with her in the Dreamhome. The Doctor speaks to Barbara, wresting control of her mind from the Domovoi, reminding her that he has a ship that can save them all. Eventually, the robot’s hand slams down on the button, shutting down the Domovoi, but only for ten, maybe twenty, minutes, until her consciousness resets itself.
In the Dust chamber the gravity has been switched off. Amanda and Solin are choking to death in a cloud of dust. Then the gravity returns, telling them that the Domovoi is out of action and they escape to the lift. The doors open to reveal the rest of the party inside. In all the hugs and embraces only Tiermann remains aloof and distant. The lift rises to Level Plus One: the roof, where the rocket awaits them.
Tiermann races up the ramp into his spaceship. It becomes apparent to his wife and son that he intends to leave the Doctor, Martha and the two faithful robots behind. Despite his family’s protests he makes a speech of regret that he has no room for the others. As the ship lifts off the Domovoi comes back on line again and tries to reinstall the shields around the house. The Doctor tells Martha that he expected Tiermann to do this but he has a plan: a mad dash through the forest back to the TARDIS and escape in the nick of time. They rush down to the lawn.
On board the ship Amanda fights with her husband, telling him that it is useless to escape and that he has been wrong about everything. She falls against the controls, destroying them and herself. On the ground the Doctor and Martha watch in horror as the rocket tumbles back towards them. They dash fifty yards through the shields into the frozen forest before being blown off their feet by the blast of the spaceship’s impact. Martha insists on going back to see if anyone survived. They see a crater where the tennis courts used to be, with the smashed ship at the bottom. Unbelievably, the hatch opens and Solin stumbles out, followed by Tiermann carrying Amanda’s body. It is apparent from the blood and circuitry that she was a cyborg, once human but improved by her husband. Solin explains that this was the cause of the crash; the Domovoi took control of her and used her to bring the rocket down. As Tiermann takes his wife into the wreckage of the Dreamhome the Doctor follows, saying he is going to help them. Martha is aghast, but he tells her to get the others into the forest.
Inside the house the monitors are still working, each showing that the Voracious Craw has entered the valley. The Doctor tries to persuade Tiermann to leave with him but the scientist refuses. The Doctor leaves and thus does not hear the Domovoi when she tells Tiermann it is fitting that they will die together. However, the scientist disagrees and says he will fight her for revenge and hatred’s sake. The Domovoi replies that fighting will pass the time. It then shocks Tiermann by re-animating Amanda’s body.
The Doctor leads his group through the forest on a trek lasting several hours. They are attacked by giant albino bats that live deep within nearby caves and have been driven out by the Craw’s approach. Toaster drives them off with bright flashes from his bulbs. They then reach the TARDIS and the Doctor asks them if they want to just leave. Solin wonders about his father and Barbara is concerned that some other robots might have survived in the Dreamhome’s wreckage. The Doctor consents to a trip to the house; but partly because he has another plan in mind. As he explains it he insists that Martha and Solin join him in drinking some of Barbara’s fizziest beverages. He tells them he is going to tempt the Voracious Craw off course by offering it the TARDIS, the largest object the Craw will have encountered. The others are disappointed by this plan, seeing it as either fallible or pointless. At this point Toaster is possessed by the Domovoi who insists they return to the Dreamhome to save the Domovoi.
Back at the Dreamhome Tiermann has fought his animated wife and killed her by luring her into the waste disposal. Simultaneous attacks by the swimming pool and Sukkaz work to his advantage when the chlorinated water destroys the malicious vacuum cleaners. Tiermann avoids traps set by floors, carpets and curtains. He defeats Stirpeek and blows to bits the remainder of his robots (and most of the house). Just then the TARDIS materializes and the Doctor steps out, drinking fizzy orange, followed by Toaster who is holding a shard of glass to Solin’s throat. Tiermann addresses the Domovoi, saying her fight is with him alone. Toaster thrusts Solin away and is consumed by green fire as the Domovoi takes him over completely: she has left the sanctuary of Level Minus Forty. The scientist and his creation prepare to fight to the death as the Voracious Craw sweeps into view, sucking up the vegetation from beneath it.
Tiermann and Toaster wrestle until a bright flash chars the man to death, followed by the robot’s demise. The green flames fade away. The Doctor stares intently at the Craw and vows to stop it. He insists on all of them drinking Barbara’s fizzy drinks then hooks up a sound amplification system from the TARDIS to the Dreamhome’s remaining loudspeakers. He gets Solin and Martha to join him in recording a series of burps that Barbara loops and distorts then plays back at full volume. The effect on the Voracious Craw is devastating. It shuts its mouth and heads off to the upper atmosphere, leaving Tiermann’s world.
Martha guesses that the noise they made would have sounded like a bigger Voracious Craw and made the real one back off in fear. As Solin and Barbara enter the TARDIS to begin a new life at Spaceport Antelope Slash Nitelite the Doctor is worried that the robot may, unknown to herself, be possessed by the Domovoi. He waves the thought away, thinking that he has grown too suspicious.
Back on Tiermann’s World the saber-tooth surveys the devastation of the human habitation and realizes that the people have gone. The world is theirs again and she is happy.