An up-and-coming young duellist named Keefer spots a sniper waiting for him on the side of the R4 motorway. Fortunately, he has disengaged his runner from traffic control for the thrill of driving it himself, and he is thus able to catch the assassin off guard and run him down. Upset by the unprofessionalism of the undeclared challenge, Keefer nevertheless contacts his agent, Jerro Fanson, to find out if they can get coverage of the kill. Fanson promises to do what he can, but warns Keefer that the main story tonight is the death of a prime duellist, Starvil, who just lost to an anonymous spot challenge. While Keefer waits to hear back, Fanson contacts Michaelson, the sports editor of Zone Three, only to learn that Michaelson has already received word that Keefer accepted the challenge and was killed on the roadway. Before they can find out what’s going on, Michaelson turns up dead and Fanson is charged with his murder. Fanson chooses to face a computer interrogation, confident that it will prove his innocence, but is unaware that the computer is registering his claims of innocence as outright lies...

The Doctor detects a fault in the TARDIS as it tries to create a space for itself in a new time continuum. The discontinuities iron themselves out with difficulty, and when the Doctor emerges, he is somewhat disorientated, not yet settled into this particular time and space. Leela gets ahead of him as they explore their surroundings, and they emerge from a tunnel into an arena marked with bloodstains. As they examine the stains, they are confronted by a security guard named Jarvis, who accuses them of defiling the sacred arena and challenges the Doctor to a duel. The Senior Umpire observes the confrontation and orders them to remain still until he’s arrived to sort out the situation. Jarvis nevertheless prepares to draw his gun and shoot the Doctor, but Leela intervenes, overpowering Jarvis and breaking his arm. When the Senior Umpire arrives, he is shocked to see that Leela has fought Jarvis but allowed him to live. When Leela refuses to kill without a reason, the Senior Umpire declares the contest void, shoots Jarvis in the head, and places both Leela and the Doctor -- whom he assumes to be her manager -- under arrest.

While waiting for Fanson to get back to him, Keefer examines the body of his challenger -- and discovers that it’s an android. This was not a spot challenge, but a deliberate murder attempt, and only two people in the settled planets are rich enough to send an android killer after him. Keefer plants an incendiary pellet in his runner and takes cover; as he’d expected, a jet-copter arrives to finish the job, but the pellet sinks into the gas tank and the runner explodes, taking out the copter. Keefer hides in the nearby woods until dark, but, also as expected, there are men with guns waiting for him when he tries to leave. Fortunately, they are not professional killers, and Keefer easily tricks them into shooting at each other and takes out the survivors. Their unprofessionalism indicates that they were just a squad of thugs sent in as backup in case the android and the copter failed to kill Keefer. Hoping that this was the last level of redundancy in his enemy’s plan, Keefer copies the thugs’ thumbprints, steals their wallets, burns their bodies and heads for the spaceport.

The Doctor and Leela are put in a well-furnished waiting room at the Court of Attack and are fitted with wrist and ankle bracelets that will contract and sever their hands and feet should they attempt to escape. They have been placed in the same cell as Fanson, who is shocked to learn that Leela deliberately allowed her opponent to live; for such a crime, she could be skullcapped and set loose on an open contract. For his part, the Doctor is surprised to learn that Fanson is here for committing murder while Leela is here for refusing to do so. Half horrified and half intrigued by Leela’s “crime”, Fanson agrees to help the Doctor come up with a defence, and suggests that he claim that the kill was delayed in order to attract attention to his fighter; if this is the case, then the Senior Umpire terminated the duel prematurely. The Doctor is unwilling to play along with the twisted rules of this society, but realises that this may be his and Leela’s only chance of getting out.

From past experience, Keefer knows that the slightest disturbance on spaceport grounds will bring out the security forces, and he intends to take advantage of that chaos. Keeping low to the ground in order to trick the automatic security scanners into believing he’s a stray dog, Keefer plants incendiary pellets in the ground and then begins firing at the scanners. Within seconds, the grounds are shrouded with smoke and the overloaded scanners conclude that there is a high probability of a terrorist attack. The Shift Controller sends out three teams, but as they enter the area, the explosive pellets go off, causing further confusion. The panic-stricken Controller orders his teams to withdraw and sends in a fourth team led by security operative Sita Benovides with orders to strafe the entire area and kill whoever’s there. In the smoke and confusion, however, Keefer overpowers one of the lone guards, knocks him out and takes his uniform. When the guards are recalled to base, Keefer slips away from them and enters the spaceport terminal, unnoticed. There, he cycles tickets and refunds through the IDs and credit cards of the thugs who were sent to kill him earlier, ends up with a Class A ticket in the name of Norbert Lung, and bluffs a counter girl into letting him aboard the first flight to the Hakai Orbital Transfer Station without first checking his picture ID.

Fanson is disturbed when he returns to his cell after his secondary court appearance; he was advised to rely on the infallible computer for his defence, but for some reason he has not yet been released. Concerned that he and Keefer have been targeted by someone powerful, Fanson asks the Doctor for a favour in exchange for his help in preparing Leela’s defence; if something happens to him, he wants the Doctor to find Keefer and warn him of the danger. The Doctor just wants to get out of this twisted world, but Leela gives her word to Fanson as a warrior. Relieved, Fanson helps the Doctor to prepare for his open court appearance, warning him not to do or say anything that could be mistaken for a spot challenge. He is then called away for his final judgement -- and is horrified when the Judicial Therapist reveals that the computer has found him guilty of murder. Since Fanson still insists that he didn’t commit the crime, the Therapist judges him homicidally insane, and he is sentenced to be skullcapped, an electronic lobotomy that effectively leaves him a living vegetable.

The Doctor and Leela are summoned to the Court of Attack, where the incident in the arena is replayed from every possible angle so the court can judge Leela’s actions. The Doctor accepts that the challenge was issued and accepted, but reminds the Court that Jarvis continued with the duel even after the Senior Umpire called a halt to proceedings. However, he then learns that the Senior Umpire never appears in playback, since he embodies the Law and the Law cannot be questioned. Since this means that the Doctor is unable to replay the critical evidence, he has no choice but to fall back on Fanson’s plan and claim that the delayed kill was a cunning strategy. The Court votes on the case and unanimously decides to accept the Doctor’s claim. He and Leela are thus freed. The Doctor now wants to get as far from this appalling society as he can, but Leela refuses to break her word and insists upon remaining to find Keefer and warn him of the danger he’s in.

Keefer reaches the Hakai Industries Orbital Transfer Station; from here, he can go anywhere in the settled planets. However, since one of the two richest people in the system is trying to kill him, he realises that there’s nowhere he can hide, and he decides instead to pick one of the two and take the fight to them. He is attacked by a mugger while booking a flight to the Geewin system, but he easily overpowers and kills the man, swaps IDs with him, dumps his body in a restroom cubicle and boards his flight. However, he has chosen his target based on the first flight to leave the Hakai OTS after his arrival -- and it hasn’t occurred to him that this could have been predicted and planned for.

Sita Benovides is not really an ordinary security guard; she’s a Major in the state security division, working undercover to investigate corruption and smuggling at the spaceport. She eventually works out that someone staged the “terrorist” attack in order to slip into the spaceport unnoticed, and vows to find out who did so, feeling that she’s been made to look a fool. However, when she reports her theory to the State Security Minister, he dismisses it as ridiculous and orders her not to investigate. She does so anyway, and becomes all the more determined to prove herself right when her fellow security operative, Lars “Driftkiller” Ronick, scoffs at her single-mindedness. Nevertheless, he supplies her with information that helps her to trace the perpetrator from the incident on the motorway up to the Hakai OTS; however, the more she learns, the more she comes to suspect that she’s stumbled across a dangerous conspiracy...

The Doctor and Leela visit prison control to ask about Fanson. The clerk on duty, Bazza, is delighted to help, as it seems the Doctor and Leela have become overnight celebrities following their unique trial. Bazza reveals that Fanson has been found guilty and skullcapped, but can’t explain why he would have chosen trial by computer if he was actually guilty. The entrance is blocked by the press and Leela’s new fans, who are eager to get a glimpse of this mysterious new fighter, and Bazza’s supervisor thus arranges for a driver to pick up the Doctor and Leela at the back door. Instead of driving them where they want, however, the driver kidnaps them and takes them to a run-down part of town, where he introduces them to his son, Benron; Benron wants to become a duellist but doesn’t really want to kill anybody, and his father, Nenron, believes that the Doctor’s new training style is just what his son needs.

The Doctor decides to play along, on the basis that becoming more rich and powerful in this society will place him in a better position to track down Keefer. To this end, he establishes a training school, enlists a number of fighters and gets himself and Leela invited to the well-publicised Maidenly-Baloch duel, where he mingles with other powerful and important spectators, such as the State Security Minister and Sita Benovides. For some reason, Maidenly doesn’t show up, and the desperate sponsors throw the court open to spot challenges. The Doctor and Leela watch in disgust as the sadistic Baloch slowly tortures and kills his opponents -- but a pale, red-haired woman then enters the ring, decapitates Baloch on her first pass, and then disappears without claiming her prize.

Keefer’s flight takes him to Piran, a satellite of the gas giant Geewin; on the way, he bribes his shuttle pilot, Melly Finbar, for information on the Lady Hakai’s personal ship, the Ultraviolet Explorer. His fellow passengers are maintenance workers and a pale, red-haired woman who does not smell of sweat. The maintenance team are jealous of Keefer, assuming him to be a rich tourist; he thus tarries deliberately in customs, letting the bureaucracy grind slowly so the other passengers will get ahead of him and he won’t get into an attention-drawing fight. Once through customs, however, he is reunited with Finbar, who tells him that the others who came in on the shuttle with him have been killed in an apparent freak accident. Finbar offers to help Keefer get aboard the Ultraviolet Explorer, and once bribed sufficiently, he smuggles Keefer into a shipment of lecea seed and fiddles the cargo manifest so that nobody will notice the weight discrepancy.

Leela becomes convinced that the Doctor is just amusing himself and has lost sight of their purpose; she is subsequently furious to learn that he’s set up a perimeter around the training compound to prevent her fans from getting in to see her, as she feels that he’s made her a prisoner without her being aware of it. She thus decides to track down Keefer on her own, and approaches a fellow fighter, Meta, to ask where she could run to if the Doctor’s radical new fighting-without-killing technique does not work out. He suggests that anyone who wanted to flee would head for the Hakai OTS, and Leela enlists Nenron’s help to get to the spaceport. On his advice, she disguises herself as a cleaner so as not to attract attention. She is separated from Nenron when they enter the main spaceport terminal, and when she spots someone following her, she dons her cleaner’s mask -- only to discover that it’s been filled with nerve gas. Paralysed, she is unable to resist as two men approach her and guide her away; they have been hired to kidnap her, but if the plan goes sour they intend to sell her on the open market.

The Doctor tries to enlist in the Guild of Agents, but its Enforcer is unable to enlist him without an official ID. The Doctor thus visits the State Security Minister, whom he met at the Baloch duel, and the Minister agrees to sort out the “bureaucratic error” that left the Doctor with no ID. In the process, the Doctor casually questions the Minister about Keefer, and realises from his reaction that he is involved in the conspiracy. The Doctor does not press him any further, and returns to his training compound only to find that Leela has gone missing. Meta tells him that Leela was asking about places to run to, and Benron discovers that his father gave Leela a ride to the spaceport -- and neither has been seen since.

Sita is placed under arrest after asking too many questions about the incident at Spaceport Main. To her shock, the Minister tells her that she’s up on charges of corruption and murder, and that the evidence against her is overwhelming. She believes at first that this is all a big mistake, but Lars Ronick then visits her in prison and flatly informs her that she’s going to be found guilty and skullcapped. However, she was picked up shortly after speaking to him, and as he doesn’t want people thinking that he turned her in, he is willing to help her escape. Nenron’s body then turns up, and Ronick visits the Doctor to question him about the death. Nenron was involved in the corruption that Sita was investigating, and he was last seen with Leela, who has since disappeared; thus, Ronick has concluded that the Doctor and Leela, like Sita, are undercover state security agents. The Doctor realises that Ronick has come to him for help, and decides to play along in the hope that Ronick will help him find Leela.

Keefer relaxes himself, using his training to lower his body’s metabolic rate so he does not need to eat or drink while the supply ship takes him to the Ultraviolet Explorer. The journey takes 136 hours, and once he arrives, he enters the ship through its loading bay and begins to search the ship methodically for the Lady Hakai. He encounters several of her bodyguards, the sumo-wrestler-type “Fat Boy” hakai-warriors, and kills each one he meets; however, he eventually concludes that this tactic is getting him nowhere, and decides to seize control of the bridge and lure the Lady Hakai out of hiding. To his surprise, however, the “flight deck” proves to be empty. He is then confronted by an android who reveals that Keefer has been manipulated into coming here, and Keefer realises too late that the android has been keeping him talking and distracted while the room fills with nerve gas...

Leela awakens to find herself weightless in a padded cell aboard a spaceship. The pilot is in a separate flight deck, beyond her reach, but he’s used to being alone and tends to talk too much. Leela thus learns that the two men who kidnapped her from the spaceport are now dead, that the pilot is being paid to transport her safely, that she’s expected to turn up alive -- and that there are a lot of things that can go wrong on a ship such as this. She thus convincingly fakes an injury, and the pilot is forced to enter the cell to find out whether she’s bluffing or not. He’s wearing a spacesuit when he enters the cell, and when Leela attacks him, the helmet twists at the wrong angle and snaps his neck. Now Leela is stuck on a ship with no pilot and no idea where she’s going -- and when she realises that the door to her cell is an airlock, she realises that she’s going to have to wear the dead pilot’s spacesuit to leave her cell, even though he soiled himself when he died. Fortunately, it turns out that he was just wearing the suit as a precaution because he didn’t know what was wrong with her, and the ship’s navigational controls are basically automatic. Unable to change course or find out where she’s going, Leela decides to take a nap so she’ll be fully rested when the ship completes its journey.

Ronick bribes a prison guard to let Sita escape, and although her wrist and ankle bracelets eventually begin to contract, the Doctor uses his sonic screwdriver to counteract the signal until Ronick can cut them free. They return to the Doctor’s training compound to plan their next move, only to find it mysteriously deserted. The Doctor enters alone and finds security guards waiting to arrest him for the murder of Pet Sanderonne and Raf Lee, the two men who kidnapped Leela from the spaceport. The Enforcer of the Guild of Agents assures the Doctor that he’s arranged for him to be tried by the Court of Attack rather than in a public criminal court, but the Doctor realises that this must be what happened to Fanson. Before the Doctor can be taken away, however, Ronick enters and bluffs the other police into believing that the Doctor is his prisoner, and the other police reluctantly release the Doctor into Ronick’s custody.

Now certain that the conspiracy centres around the missing Keefer, the Doctor, Sita and Ronick follow their only lead to the Hakai OTS. There, Ronick goes through his underworld contacts to reach Melly Finbar, who offers to take them to Keefer for a price. Once they’ve left the OTS, the Doctor tricks Finbar into admitting that they’re going to the Ultraviolet Explorer; the Lady Hakai normally spends her time in orbit around Geewin, but for some reason her ship is now approaching the OTS, which means they reach the ship much more quickly than did Keefer. Finbar claims to have no idea why Keefer wanted to get aboard the Lady Hakai’s ship, but the Doctor notes that he seems too relaxed for someone who’s about to dock illicitly with the home of the richest woman in the system. When they dock with the Ultraviolet Explorer and board, Finbar puts on a show of watching out for guards, but the Doctor eventually calls his bluff, accusing him of knowing exactly where they’re going. Finbar protests, but a party of hakai-warriors then steps out of hiding and captures the Doctor and his allies.

Leela’s ship also docks with the Ultraviolet Explorer, and when she emerges to investigate, she is captured by hakai-warriors and brought to a perfect replica of the Court of Attack. Here, she meets the Lady Hakai, an elderly woman who has undergone extensive surgery to make her appear young and beautiful. Realising that the Lady Hakai is the one responsible for her kidnapping, Leela challenges her to a duel, but the Lady is too rich and powerful to take her at all seriously, and indeed seems to regard her as a plaything. The Lady orders her people to bring her Keefer, who has been kept helpless and weightless in a grain hopper since he was captured; however, when the technicians try to remove him from the hopper, he surprises and overpowers them, killing them and the hakai-warriors sent to collect him. He then heads for the engine room, where he is confronted by the android who captured him; however, when he asks the android where the ship’s pseudo-grav generator is, the literal-minded android answers him, and Keefer sabotages it, knocking out the ship’s gravity. He then sets off to confront the Lady Hakai as the android tries to repair the damage.

The Doctor and his allies are brought before the Lady Hakai, but the gravity goes off as she orders the Doctor to set up a duel between Leela and Keefer. Leela takes advantage of the confusion to attack the Lady Hakai, but the android repairs the damage and restores the gravity before Leela can kill her. Keefer then arrives, and when the Lady Hakai orders him and Leela to fight for her amusement, the Doctor concludes that she’s just a wealthy fan who regards the duellists as her private toys. He tells the others to wait in the corridor while he negotiates, but Hakai, believing that they will attempt to escape, shoots and kills Finbar; he’d been paid to bring them all to her, and she assumes he’s the only one who can take them away. However, the Doctor watched him pilot the ship on the way here and is aware that it’s not as difficult as he made it seem; while the Lady is distracted, therefore, he ushers the others back to the ship and pilots them back to the Hakai OTS. When they discover that Leela’s knife has been placed aboard Finbar’s ship, however, the Doctor realises that they’re still being manipulated... and he doubts that Ronick is still helping them out of the goodness of his heart.

Back on the Hakai OTS, the Doctor learns that these recent events are turning the people of this society against the barbaric nature of the Court of Attack and the duelling leagues. When he and his allies return to Spaceport Main, two spot challengers try to shoot Keefer and Leela, and they realise that an open contract has been declared on them both. They return to the Doctor’s training compound to plan their next move, only to find that it’s been looted and that the TARDIS has been stolen. With no other leads, the Doctor turns on Ronick, demanding to know who he’s really working for. Ronick protests his innocence, but when Keefer challenges him to a duel, this gets the Doctor thinking, and he comes up with a plan to expose the conspiracy: he will allow Keefer and Leela to set up a duel in the arena for the Lady Hakai to watch. Ronick must use his contacts to ensure that the league officials are there, and the Doctor will try to trick the Lady Hakai into confessing the truth in front of them.

Since the duel is only for show, the Doctor orders Leela and Keefer not to fight; however, Leela’s lack of respect for the sacred arena infuriates Keefer, who grows more and more angry as she scoffs at his deep-held beliefs. Meanwhile, the Doctor is sitting in the Court of Attack with a number of important league officials, including the Lady Hakai, the State Security Minister, and the Enforcer of the Guild of Agents -- but his plan goes awry when he realises that everyone in the room is part of the conspiracy. They too believe that the duelling leagues are barbaric, and they have been sending out androids to kill off the main duellists in order to bring the system down. Though the Doctor agrees that the system of legalised murder is appalling, he refuses to let the conspirators commit murder to stop it; however, Keefer then snaps and challenges Leela to a genuine duel, and the conspirators hold the Doctor back, preventing him from interfering.