Glavis Judd, interstellar warlord, has just captured the capital city of the planet Esselven. Judd is a particularly dangerous man, who uses his intelligence to observe and reinforce his targets’ weaknesses. Born in obscurity on the planet Zalcrossar, he exercised his mind and body, joined the military, bided his time and took control of the planet so gradually that few noticed he was doing it. In order to keep his people occupied and expand his power base, he secretly fomented revolution on the neighbouring planet Gadron, making it seem as though the government was responsible for the failing social order; the people of Gadron actually invited him in, to dispose their corrupt leaders. His Protectorate has been expanding ever since, and recently he’s allowed the amoral reporter Dexel Dynes to report on his conquests, in order to shape the media presentation of the Protectorate to his advantage. To Dynes, still smarting from the Gelsandor fiasco, Judd is a dream come true -- and Judd is planning to use what he learns from Dynes to manipulate the media in Dynes’ sector of the galaxy, when the time comes for him to conquer there as well.

However, all of this comes to a halt on Esselven when Judd gives the royal family a chance to surrender peacefully. Instead, they escape to their private shuttle, and jump into hyperspace while still dangerously close to the planet’s gravity well, risking damage to their ship’s engines. When Judd breaks into the palace, he finds that King Hathold has destroyed almost all copies of the planetary computer network codes, which Judd requires to restore social services. Without these codes, social order will begin to crumble, and the people of Esselven will blame Judd. The only surviving copies of the codes have been sealed in an impenetrable vault which will only open for members of the Esselven royal family. To preserve his Protectorate, Judd must find out where Hathold and his clan have gone.

The TARDIS materialises in a beautiful garden estate, where a large red sun hangs motionless in the sky. As the Doctor attempts to coax information from the recalcitrant TARDIS systems, Peri explores her surroundings and meets a giant teddy bear named Boots. Boots hides while she’s fetching the Doctor, and as they search for him, they spot a troupe of travelling actors who seem to have walked right out of a Shakespearian play. Boots then reappears, and leads Peri on a wild chase across the gardens -- and deliberately tricks her into falling into a haha, a pit meant to protect the estate from wandering animals. The Doctor realises that this apparent paradise is flawed; Peri could have been seriously injured, and the haha has been improperly constructed, sitting as it does in the middle of nowhere without actually blocking anything.

In the palace of Aldermar, Princess Oralissa is caught in a dilemma. She swears she will marry only for true love, but her parents insist that, for political reasons, she must choose either Prince Benedek of Corthane or Duke Stephon of Eridros. Oralissa feels weighed down by a sense of doom, but as she confines in her personal maid, Hatty, she is attacked by a mischievous brogle, which flings pebbles at her, stinging her arm. Nothing like this has ever happened to her before, and the incident gives her hope that perhaps her future is not predetermined after all. But when Benedek and Stephon arrive, the polite rivalry between their countries turns to bitter personal jealousy when they catch sight of the beautiful Oralissa and both fall in love instantly. This contest is now in deadly earnest.

The Doctor returns to the TARDIS for rope with which to rescue Peri, only to find that his ship is missing. While he’s gone, two gardening robots find and rescue Peri, initially assuming her to be a lady from the Palace. However, when she incorrectly identifies one of the flowers in the garden, they conclude that she must be a scavenger. She is thus punished by being put to work with the other scavengers, primitive people from the wild woods who occasionally raid the gardens for food. Most of the other prisoners have lost the will to fight, but one young man, Kel, is still defiant. Peri tries to learn about this planet from him, but he knows nothing of other worlds; no stars are ever visible, as one side of the planet is bathed in perpetual warm sunlight, while the dark side is shrouded in clouds and twilight. According to legend, Kel’s people angered the sun god, and were expelled from the gardens by the Lords’ warriors though they pleaded for forgiveness. Peri vows to escape, with Kel’s help -- but how can they get past eternally vigilant robots?

Searching for the TARDIS and Peri, the Doctor instead encounters a little girl, Luci Longlocks, who claims that she’s there to play games with children. Although Luci behaves somewhat oddly, the Doctor convinces her to lead him to a place where children are forbidden to play, and thus locates an entrance to the underground service tunnels. Unable to enter, Luci departs to look for children, while the Doctor enters the tunnels and finds the TARDIS. He is then attacked by gardeners who believe him to be a scavenger, and is badly injured while hiding in a compost hopper which unexpectedly drops him into an underground train. He recovers to find himself being treated by a friendly gathering robot, Green-8, who developed a sense of self-awareness because of a malfunctioning repair subroutine. It rescued the Doctor because it wanted someone to talk to; no other robots share Green-8’s sense of self, the Lords apparently regard the robots as beneath notice, and the scavengers all run away when it approaches them. Green-8 identifies this world as Esselven, and explains that it is ruled by the Lords from the Summer Palace. The Doctor in turn informs Green-8 that its paradise is flawed, and Green-8 promises to help him track down his missing friend Peri, on the condition that Green-8 be allowed to accompany him and learn more about the possibilities of sentience.

Outside the gardens, a year has passed since the fall of Esselven, and Judd believes that he has finally located the royal family’s bolthole. He presents his case to Dynes as though the family are cruel tyrants, he is the benevolent liberator, and those who tried to protect the family’s secrets are the victims of misguided loyalty; Dynes isn’t fooled, but it makes for good press. Judd’s battle fleet now surrounds the royal family’s private retreat, a small planetoid orbiting a white dwarf star and protected by a force field stronger than anything Judd has ever encountered. The entire fleet concentrates its firepower on the shield, but the only result is a relatively small discontinuity which opens up in the polar region. Dynes’ ship, the Stop Press, is smaller than any of Judd’s landers, and he thus passes through first, hoping to get background for his story; Judd allows him to go, as he can do no harm and may draw fire away from Judd’s forces.

Peri soon determines that the only way to cut her bonds and escape is one the guards’ gardening tools, and tries to convince Kel to fight her as a distraction. This fails when Kel, unused to strong and forthright women, reacts inappropriately to being tackled by her. As Peri tries to come up with another plan, the sky suddenly ripples with light and a windstorm tears the garden apart around her. In the ensuing confusion, Peri and Kel steal a tool from a damaged gardener, cut their bonds and escape. Elsewhere, the Doctor recognises the windstorm as an attack on a planetary defense shield, and realises that he must trust Peri to take care of herself while he travels to the Summer Palace to find out what the Lords are doing about this. As Green-8 co-ordinates repairs in its sector and the Doctor builds a disguise which will enable him to pass by the other gardening robots, the Doctor ponders what Green-8 has told him about this world. Apparently, the robots stopped delivering food to the Winter Palace some 300 years ago, and it has been isolated ever since. Is this significant?

Oralissa walks in the grounds of the palace with her suitors, but is disturbed by their talk of love and tries to turn the conversation towards the strange windstorm. However, nobody else wishes to talk of such matters, and even she finds it difficult to maintain her curiosity. But when she sees strange mechanicals in the grounds, which appear almost like soldiers, obvious questions occur to her. Her palace has many mechanical servants, but what exactly are they? Where did they come from? Who constructed them? Why do her parents, servants and suitors dismiss these questions as beneath their notice and forget they’ve ever been asked? Perhaps most importantly, why is Oralissa the only one who finds any of this even slightly strange?

Peri and Kel find it easier to hide from the gardeners amongst the damaged gardens, but more gardeners have been sent out to repair the damage, and they must find somewhere safe to spend the night. Peri convinces Kel to sleep in a long-abandoned folly, despite his deeply ingrained fear of trespassing in the Lords’ buildings; however, she must then reject his clumsy advances, and explain that she isn’t like the other women he knows. Luci Longlocks unexpectedly appears in the folly and asks if they want to play a game, and although Peri also senses something odd about the girl, she convinces Luci to play a game called “Dodge the Gardener” with them. Luci thus plays the lookout, helping Peri and Kel to reach the woods safely. There, Peri sees automated earthmoving machines planing the land absolutely flat rather than landscaping a variety of gardens around its contours. Luci finds herself unable to enter the woods, but as she goes, she compares Peri favourably to the Doctor -- and when Peri tries to stop her to learn more, her hand passes straight through Luci’s arm. Luci was a hologram all along.

The Doctor disguises himself as a Green-sector robot, and as Green-8 tests him on the proper responses to give to questioning, he realises that Blue and Red sector robots show an unfounded bias towards Green robots based on a non-existence hierarchy. This is further evidence of uncorrected glitches in the robots’ control network. As the Doctor and Green-8 head for the Palace, they encounter a group of scavengers being worked to death with minimal rations, and the Doctor, infuriated, convinces Green-8 to help him distract the Red-sector guards and free the prisoners, although this means risking delay and capture. They succeed, and most of the scavengers are grateful, even though some no longer understand the concept of freedom.

Dynes passes through the discontinuity in the planetary shield, although the distortion within the passage nearly causes him to lose consciousness. Once inside, he’s surprised to meet no resistance, and when he eventually locates the planetoid’s spaceport it appears to have been long-abandoned to the jungle. At first, he assumes this to be camouflage, until he finds the spaceport’s defense cannons, abandoned and rusting. An even greater mystery lies within the spaceport hangar -- King Hathold’s escape shuttle has been abandoned in a state of disrepair, and it seems to have been lying here for centuries. Strangely, Judd does not follow Dynes through the shield right away, and after waiting impatiently for some time, Dynes sends his remote cameras, DAVEs, out into the forest to gather background information for his story.

Upon entering the woods, Peri and Kel are attacked by a pack of feral dogs, but are rescued by scavengers from Kel’s home, Thorn Tree village. Kel is welcomed back, and Peri is questioned by the village Chansor, Greld, who is taken aback when she urges him to stand up to the cruel Lords and demanding an explanation for his people’s treatment. Exhausted by her experiences, Peri agrees to accept a “b’long,” a bracelet which marks her as a member of Thorn Tree village and allows her to sleep there for the night. However, Kel then claims that escaping from the gardeners has proven his manhood, which means that he can now choose a mate. He chooses Peri. Peri objects, and, realising that Kel’s choice has upset a Thorn Tree woman named Nerla, urges Nerla to stand up for herself. This backfires, as Nerla challenges Peri to fight for Kel.

The Doctor and Green-8 arrive at the Summer Palace, where two guards in surprisingly primitive attire absently wave them through, as if robots are beneath their notice. In the grounds of the Palace, they spot other robots which seem to be preparing for battle, but when they enter the Palace itself through the servants’ entrance, they find only a teeming kitchen staffed by human servants. The Doctor finds something odd about the scene, but isn’t sure what it is. They continue on to the dining hall, where the Doctor emerges from his disguise and tries to warn the King that his world is under attack; however, the King is angered by the interruption and orders his guards to take the intruder away. The Doctor retreats inside his robot disguise to protect himself -- and the guards, mildly surprised, immediately forget that he was there at all. Surprised, the Doctor and Green-8 realise that these people, whoever they are, can’t be the Lords who created this world. They return to the entrance hall, where they reason that the mechanical servants’ entrance must be hidden to preserve the illusion of the setting, and work out its location behind a holographic wall. A secret lift carries them to the service areas beneath the Palace, where they find that someone or something is responding to the attack on the planetary defense shield. But it can’t be the Lords, for beyond this chamber is another, containing dozens of mummified bodies.

Peri is forced to battle Nerla, but just as Nerla is about to kill her, a DAVE arrives, sending the villagers into a panic. Dynes recognises Peri from Gelsandor, as she recognises the DAVE. She realises that Dynes doesn’t know much about this world, but deduces that he must be here on a story; thus, she offers to trade information in exchange for a great story about the Lords’ cruel oppression of the scavengers. Dynes thus tells her about Judd, and she realises that the primitive scavengers can’t possibly defend themselves against what’s coming. The villagers, who are now in awe of Peri, agree to warn the other villages about the threat and hide from the invaders, while Peri takes Kel, Nerla, and their friend Raz to the Summer Palace to seek out the Doctor and defend themselves against the attack. Dynes sends some of his DAVEs with them to obseve as they steal a landscaping machine and head for the Palace.

Judd finally passes through the discontinuity, although two of his landers are destroyed when they hit its fluctuating walls. When Judd contacts Dynes, Dynes is surprised to learn that only five minutes have passed outside the shield since he entered -- two days have passed for him inside... Setting this aside for the moment, Dynes shows Judd an edited verison of his encounter in the village, glossing over the mystery of Peri’s appearance while directing Judd towards the Palace, in order to get things moving more quickly and make a better story. As the Palace is clearly the centre of operations here, Judd decides to attack it immediately.

In the dining hall of the Palace, Oralissa is struggling to hold onto her memory of the man who “disappeared” by climbing into a robot; everyone else already seems to have forgotten that it happened. She excuses herself and leaves the dining hall, trying to find the stranger in the hope that he will tell her what is wrong with her world. When she fails to return, the others set off in search of her, but as more and more time passes with no results they begin to become concerned. Eventually, Stephon makes a snide remark about Benedek’s treatment of the princess, and tempers flare. When Oralissa returns, the rivals are preparing to duel to the death, and she is unable to prevent them from doing so; as she’d feared, her fate is not her own.

In the depths of the Palace, the Doctor and Green-8 find another room, where the Doctor notes some odd characteristics of the planetary shield, and is disturbed to realise that the defense against the planetary attack is entirely automated. Green-8 discovers an “imaging” subsystem drawing power away from the other systems, and the Doctor realises that the Palace is largely a holographic illusion built around a simple framework. He also realises that, despite the bustling activity in the kitchen, he couldn’t smell anything cooking. When he switches off the subroutine, much of the Palace disappears -- as do its occupants, including Benedek, Stephon, the King and Queen, and the terrified Oralissa. They were only characters in an interactive drama called The Princess of Aldermar; even Luci and Boots were holographic nannies, programmed to play games with the real Lords’ children.

Peri and the scavengers arrive in the Palace, and the Blue robots open fire on them, destroying the DAVEs. Green-8 manages to shut down the Blue robots, however, and Peri is thus safely reunited with the Doctor. When they share stories, the Doctor looks up references to Glavis Judd in the Palace’s computer, and is disgusted by what he finds. He also triggers a recorded message from King Hathold, who appears to be dying of radiation poisoning. This fills in the rest of the pieces, particularly when the Doctor notes the time code, which indicates that this message was recorded 500 years ago. This planetoid is an unusually dense world circling a white dwarf, which appears to be a red giant due to the planetary defense shield. The intense gravity had already distorted the fabric of time and space in this area, and when Hathold’s engineers tried to increase power to the defensive shield, this strained the continuum even further. Time within the shield now runs 500 times faster than it does outside.

The strain caused the nuclear reactor in the Winter Palace to melt down, and although the engineers shut down the Summer Palace’s reactor in time they were all exposed to massive doses of radiation in the process. Hathold sent his family to the woods until the radiation decayed to a safe level, but the damage to the systems had corrupted their robot servants’ programming, and when they tried to return the robots drove them back into the woods again. The glitches in the computer network have thus gone uncorrected for centuries. At some point the interactive drama must have begun playing automatically on an infinite loop, and ever since, the robots have been loyally serving illusory Lords while the real descendents of Esselven’s royal family eked out a miserable existence in the woods. And now, Judd has arrived -- and any one of the defenceless scavengers can open the vault on Esselven for him, while the temporal science he learns from studying the shield will give him a powerful new weapon with which to continue his campaign of terror.

The Doctor decides to generate a holographic animal to monitor Judd’s progress through the woods, but the hologram is replaced by Oralissa, who has fought her way back into existence from limbo. Realising what has happened, the Doctor gives her access to the computer’s data banks so she can learn the truth for herself. The characters in the play have a certain amount of artificial intelligence in order to respond interactively with real participants within the parameters of the drama, but whereas the others start over with a clean slate at the beginning of each loop, Oralissa’s memory has not been wiped entirely clean due to another glitch in the systems. Trace memories have built up over each repetition, and she, like Green-8, has evolved into a state of self-awareness. The processing speed within the network helps her to come to terms quickly with the truth about her nature -- but now the Doctor is faced with a moral dilemma, for if it becomes necessary to destroy the Palace to keep the secrets of the shield from Judd, this will mean killing the Princess.

Judd’s troops attack the Palace, and the Doctor and Green-8 send the landscaping machines, the Blue sector robots, and the holograms to fight them. Although insubstantial, the holograms can still block the soldiers’ lines of sight, and if they get close enough their floating projector units can detonate like grenades. Dynes manages to slip a DAVE past the fighting and into the control room, where he watches from hiding as Peri -- and a Doctor who looks nothing like the man Dynes met on Gelsandor -- attempt to hold off the attack. However, the secondary power systems fail, and Nerla, Kel and Raz vanish into thin air; it seems they too were holograms, generated as part of an interactive adventure in primitive lifestyles. Claiming that he’s far too late to save anyone, the Doctor takes Peri into the TARDIS and dematerialises. When Judd and his troops arrive, Judd soon works out the truth about the temporal discontinuity, but the knowledge is of no use; the power failure has triggered a self-destruct sequence, and Judd and his men must retreat empty-handed, having wasted the past year in a fruitless search. Dynes departs for well, realising that this will mean a delay to the Protectorate’s expansion, and cursing himself for investing his time in Judd instead of investigating the mysterious Peri, her shape-shifting friend and their vanishing blue box.

As soon as the coast is clear, the TARDIS rematerialises in the control room, bringing back the Doctor, Peri, and the real Kel, Nerla and Raz. With Green-8 and Oralissa’s help, the Doctor has staged an elaborate bluff, convincing Judd to retreat. As Judd and Dynes pass back through the discontinuity, the Doctor manipulates the shield to bring this world’s Time back in synch with the outside galaxy -- and as a balance must be maintained, Judd and Dynes are in for a surprise. The Doctor and Peri then depart, for real, leaving Green-8 and Oralissa to begin the process of re-educating the scavengers and preparing them to return home to the real Esselven.

When Judd and Dynes emerge from the discontinuity, 500 years have passed outside. Dynes is now a forgotten has-been, his sensationalistic, tabloid reporting style literally a thing of the past. When Judd returns to Esselven on his sole remaining ship, he is captured by a royal patrol and brought before King Kel the Third, who informs him that his heartless Protectorate fell apart soon after Judd’s disappearance. The King joins Nanny Oralissa outside with his children, while Chancellor Greeneight has Judd sent to a mental institution, along with all of the other madmen who have claimed throughout the centuries to be the infamous Glavis Judd...