Mallick runs for hours across a polluted landscape. Eventually he stumbles and falls on the rubble of broken machine parts and tears his chin on a jagged metal edge. A figure in the gloom fires an energy bolt at him and Mallick climbs away down a ladder. The figure follows while another one fires a shot from a nearby gantry. Mallick tumbles down a slope, injuring his back. The two figures close in. Mallick struggles to his feet but runs into an octopoid monster that starts to crush him. One of the pursuing figures uses his weapon - an Eradicator - to shoot the monster in the mouth. The two hunters close in. one places a pistol to Mallick's head and fires.

Harry Mossop spent twenty years in the Metropolitan Police until he lost the job two years ago. Since then he has been a security guard for Grant Pangborne but that job went too. Now he gets by on jobseekers' allowance and faces the scorn of his wife, Dora, and the disregard of his eighteen year old daughter Sophie on a daily basis. He tells his wife that he might go to see whether Pangborne will give him his job back. Christmas is coming and the lack of money is biting Harry's ego.

The TARDIS lands on a space platform that is fifteen miles in diameter. It is one of fifty such stations on the outer rim of the galaxy. The Doctor says that it is a leisure platform for the Torodons. He tells Rory and Amy that Torodon men are usually involved in heavy industrial work whereas their women are reserved for entertainment. He warns Amy that it is very much a man's world.

Harry puts on a black outfit and picks up some burglary tools. He takes a tube train to Pangborne's offices. He worked there for three months after losing his job with the Metropolitan Police. However, after trying to install CCTV he found himself out of a job. In many ways he feels that he made himself redundant.

Torodons are stocky humanoids with a silvery skin but are also lithe and graceful. The women wear figure-hugging body suits and rainbow make-up. There are many other species on the station and nobody pays any attention to the three newcomers. There seems to be perpetual rainfall on the platform but the Doctor says that it is condensation from the underside of the domed roof. He says he once got caught up in the crossfire of a battle between Torodon and their Terileptil enemies. He saved a Torodon destroyer that was in danger of blowing up and made friends with Kobal Zalu, now a police chief on the platform. He tells Amy and Rory to go and have fun while he catches up with his friend. As he walks alone to meet his friend he is arrested and told that he is lucky he wasn't shot on sight.

Harry uses the key code to enter Pangborne's building. He makes his way to the yard where he is surprised to see two trucks parked. He hears a muffled cry from one and is picked up and flung by a massive figure standing in the dark. It is a man wearing heavy-duty body armour, at least two metres tall. The man has a face split in two: one half looks smooth and healthy, the other is grey and dead. As Harry is picked up and flung again he rips his assailant's sleeve, revealing a mechanical arm.

Rory and Amy find themselves lured into a gambling casino. Everything inside is lurid and tasteless but as they turn to leave they pass what looks like a Craps game. Rory watches for a while and comments that one player's winning streak looks too good to be true. Unfortunately, his words are overheard and the player asks if Rory thinks he is cheating. When Amy tries to drag Rory away from an escalating argument, Rory's manhood is insulted. Stung, he accepts a challenge to play the game of Dead Man's Duel.

Harry is interrogated by the giant, Zarbotan, and another man, Zalizta. They want to know how much he knows about their operation. Harry tries to bluff is way out but they use a screen to contact Pangborne (who they call Xorax). He tells them that Harry is an incompetent ex-policeman. They are a little mollified but blame the security breach on Xorax and say he will be reported to Xorg. They decide to take Harry and, to ensure there is no follow up to his disappearance, his family.

Rory finds himself out of his depth in the game and losses everything. Not only that but he is informed that he must take part in a Reparation Throw. The stakes are the TARDIS, which his opponent Xaaael, has located on the casino's screens as the only non-Torodon vessel in the docking bay. Inevitably, he loses. Xaaael has him marched away to hand over the TARDIS in person. Amy leaves the casino alone. A grey-skinned janitor tells her that Rory is in deep trouble. Amy agrees - trouble with her. She enters a police station to make a complaint. A policeman calls up a camera shot of the docking bay. It shows Rory, Xaaael and several of the Torodon's henchmen. When Rory cannot produce the TARDIS key he is beaten unconscious. The policeman switches off the screen and announces that no law has been broken. Amy leaves the police station. She encounters the janitor again and asks him where Rory went. He leads her down to a store room and prises open a crate. He tells her to get in: the crate is going onto Xaaael's ship and that is where Rory will be.

The Doctor is taken to Kobal Zalu who sees that he has changed bodies. The Doctor tells him that he has changed several times since they last met. Zalu says that he wants to talk but the old days are over and he wants the Doctor to leave the platform without causing trouble. Confused and rueful, the Doctor leaves. He is back very soon, telling Zalu that the TARDIS and his friends have vanished and that the whole incident was watched by one of Zalu's officers. The Chief asks what he could do - the TARDIS was won in a game of Dead Man's Duel. The Doctor is flabbergasted but Zalu says that this is organized crime on a scale beyond the police's powers. As the Doctor prepares to storm out Zalu takes him to the Intelligence Room, telling him that there are things that he needs to know.

Back on Earth, Harry's wife Dora and his daughter Sophie are kidnapped as their car drives through Hammersmith. They are dropped into a padded chamber containing several people including Harry. Dora accuses him of getting them into this mess by unofficially investigating criminals but before Harry can offer a plausible explanation there is a thrust of power and they all suffer massive g-forces.

Zalu shows the Doctor profiles of Zargadoz Xaaael, Krauzzen Xorg and Zorbatan, among others. He explains that they are all part of Xorg's influential and powerful crime syndicate. Added to their power and ruthlessness, they also indulge themselves in 'fun hunts' where the moon of Zigriz, Gorgoror, hosts big game hunts of anything they have captured elsewhere in the galaxy.including people. Zalu says he is powerless to act because Central Government is happy for Xorg to carry on his activities on the Outer Rim and not bother them at the Inner Rim or on Torodon itself. The Doctor says that if the authorities won't intervene he will have to do it himself. Zalu introduces him to Point-Sergeant Xelos. She is the officer that Amy went to earlier. She hands the Doctor a rifle. At first he says that he doesn't use weapons but they explain that it is the only way he will get his friends back. Zalu tells him that the rifle is a transmat beam disguised as a weapon. It will look like it has disintegrated its target but in reality it will have transported it back to a holding cell on LP9. Its range will easily reach Gorgoror. Unfortunately, it is only good for three shots.

The Doctor takes the rifle and the ship that Zalu loans him. It is a police vessel that has been disguised for two reasons; so that Xorg's men don't recognise it and, if anything goes wrong, it allows the police deniability.

Amy is discovered in the hold of Xorg's ship almost as soon as she emerges from the crate. It has been transferred across from Xaaael's craft. When Xorg finds out that she has come to rescue her husband he is amused. He tells Xaaael to give her a job as a waitress in the salon.

The prisoners are unloaded into a bare room. They can't work out why they have been kidnapped but Andrei, a Romanian, says that some of them are illegal immigrants. A bloodied and bandaged Rory steps out and tells them that they are on board the Ellipsis, a Torodon star-cruiser. This information perplexes Harry but he finds it difficult to argue with the evidence. Zarbotan and two other Torodons enter with a Perspex trough of grey, sludgy protein. The captives demand an explanation but Zarbotan merely tells them that they have five minutes to eat. Rory points out that they wouldn't be feeding prisoners if they meant to kill them. He samples some of the tasteless food. Harry looks around at Rory, Sophie and Dora and then at Andrei and his group of companions. He surmises that as hostages they won't be worth much in ransom money. Rory points out that they must be valuable to somebody for all of this trouble to have been taken.

Amy is led to the salon. It is a luxurious space attended by several Torodon women. Lounging around the couches are several males. Among them is the entertainer, Zubedai, who she had seen in the casino on LP9. She is taken to a room behind the bar to meet Madam Xagra, the largest female that Amy has set eyes on. She tells Amy that she is the head housekeeper on the ship and it is her job to ensure that the female staff is obedient and attentive of the men. She adds that Amy's life will depend on her subservience. Amy looks out of the porthole and asks where they are. Xagra tells her that they are orbiting the moon, Gorgoror.

A drop ship falls to the moon's surface. It passes through toxic smog to a landscape lashed by wind and rain. It passes over a wasteland of derelict buildings and sweeps in to land in a vast structure of blackened bricks. The captives are unloaded by Zarbotan and three others. They are taken outside into the weak daylight. In front of them are ruined towers and a pool of stagnant water. Zarbotan tosses a discarded tool into the water. It dissolves immediately. Harry says that they can't be abandoned here but Zarbotan says that most visitors don't stay there for more than a couple of days: they are either eaten by the savage creatures that infest the moon or they are killed in the chase. He adds that there are seven areas in the chase before advising them to use them well and live - for a while.

Amy has spiked, rainbow hair and a skintight cat-suit. She finds it rather fetching but none of the men are paying attention. They are too much taken by the news that an unknown hunter has arrived, prepared to pay big money to join the hunt at the last minute. Krauzzen patches the newcomer, the Doctor, onto the screen. Clearly the man is in a spaceship, his boots resting on the control block. Krauzzen tells him to leave their space but the Doctor wagers that he can outscore any of the hunters on board the ship. He shows them a case full of Torodon par-creds to back up his wager. Krauzzen is impressed but the deal clincher comes when the Doctor uses his psychic paper to show a reference from Xandor Konzalar, one of the greatest champions of the hunt. The other hunters around Krauzzen agree that the Doctor should be allowed to join them.

The drop ship departs and the dispirited prisoners camp out by a huge exhaust tower. Rory grows exasperated with Harry's blind optimism that the Torodons will simply return for them in a couple of days and let them go. He makes a fire and surveys the people gathered around it. He notices that Sophie has moved away from her parents and has attached herself to Andrei. His musings are interrupted when a bipedal monster with a shaggy pelt howls in the distance and then races towards them. Rory tells everyone to run.

In the salon, the Doctor shows off his rifle, claiming to have designed it himself. Krauzzen shouts across the room to a powerful gangster, Xalva, and tells him to kill the Doctor. Before the gangster can react, the Doctor shoots him with the transmat rifle. There is a flash and the man vanishes leaving a pile of dust. This apparently satisfies Krauzzen but the fact that the Doctor has only brought a quarter of the promised money doesn't. The Doctor tells him that the rest is in his ship in the docking bay. He adds that the ship is locked with a black-light micro-circuitor that will bow Krauzzen's ship apart if anyone tampers with it. At last, the gangster leader relaxes. He feels that he has much to gain from meeting the Doctor. The Doctor is introduced to the rest of the hunters and then shown images of the prey, including Rory. He is told that they will begin the chase in twenty-four hours.

The beast bounds after the prisoners as they run into a derelict building. Harry decides that, as it can outrun them; the best way to avoid it is to climb a gantry. Sophie refuses to go with him, saying that he is always wrong, and follows Andrei and the others. Harry and Dora climb on together but the beast chases them. It is close behind when they reach the top. Just as it looks over for them, Rory shouts for them to cross a ramshackle bridge. He helps them across and then slides a crate down, followed by two more. The third sends the moon-buck plunging and it is killed, impaled on a jagged metal shard. Watching on a screen, the Doctor mutters, Poor Aggedor.' Amy sneaks up to stand beside the Doctor. He passes her a note. When she reads it tells her to find the TARDIS while he is on Gorgoror. Inside the paper is the TARDIS key.

The Doctor and the other hunters are taken by drop-ship to the moon's surface. They split into groups and begin to look for their prey. On the way the Doctor and Krelbin encounter a vast blob of vitreous material sliding towards the. As Krelbin prepares to disintegrate it, the Doctor fires his transmat rifle. The creature vanishes. The Doctor knows that he has only one shot left. Krelbin tells him that they have done well to leave the other hunters; he doesn't rate any of them. He explains that he was once a Galactic Marine. Even though he knows that Zarbotan and Krauzzen were in the elite forces he speaks disparagingly of their career paths since. He says that he only keeps in trim for when the real war starts again.

As Rory leads Harry and Dora through the complex of derelict buildings he leaves the mark of a jagged mouth, scrawled with a lump of charcoal, at every divide in the paths. When Harry asks what it is, Rory says that he hopes it will be their salvation. Soon after, they are tracked down by a giant insect. Dora is too shocked and exhausted to run and passes out, so they leave her in some lockers and confront the creature themselves. They try to ride it down with a wagon but the creature leaps aboard with them. They fight it off, Harry chopping at it with a spade, and it plunges down a gulf as the wagon picks up speed.

Back on the ship, Amy decides to take on Xaaael so that she can access the TARDIS she challenges him to a game: if she wins, she gets easier living conditions; if she loses she lets him into the TARDIS. He agrees to meet her in his quarters. Once there, she has him repeat the rules of the game over and over while simultaneously plying him with drink. Eventually, he passes out and she steals his wallet of pass cards.

Krelbin and the Doctor encounter an ape-like shologgi in a narrow passage. The Doctor says that, despite its appearance to the contrary, it is a docile herbivore. He shoulders his rifle and edges past the creature. As Krelbin follows the Doctor tells him that it was trained for gladiatorial combat and will respond to a high-pitched whistle. To prove the point he uses his sonic screwdriver to emit just such a sound. The shologgi suddenly becomes fearsomely alert. The Doctor tells Krelbin to slide his weapons over or he will whistle again and Krelbin will die. Once he has the weapons the Doctor drops them down a well and then gives Krelbin ten seconds to run before he uses the screwdriver again. In the observation chamber, Krauzzen and his gangsters watch in amazement.

Harry and Rory, scarcely believing that they are alive, make their way up from the floor of a canyon where their truck came to rest. As they walk, Harry tells how he lost his job on the police due to incompetence. Rory says that he is in this mess due to mistakes of his own. They arrive at a barricade leading to a prison facility. They enter because Harry thinks this may be a source of weapons. He is right. They find a collection of rusty bats, spears, cleavers and shields.

Amy enters the Secure Hold and starts to look for the TARDIS. She hears someone banging on a door and opens it. A Torodon male is inside. He says that he has been locked up to die in there. His name is Xorax but she might know him as Grant Pangborne.

The Doctor releases Dora from the locker where the men hid her. He tells her that he has come to rescue her and her friends. Before they leave the locker room he has her change into more practical clothes - a close-fitting anti-toxin suit. This is all watched by Krauzzen who now knows that the Doctor is not who he had claimed to be. He decides that such an infiltration requires extreme action. His men know what that entails.

Zarbotan is furious when he discovers that Xaaael has been duped by Amy. They both head to the hold.

Dora and the Doctor scramble through a series of ducts. They are being pursued by an Air-Walker, a bipedal creature with a leathery skin. They arrive in a huge chamber that, from the look of it, once contained a power plant. They scramble over debris and up onto a causeway. As they cross over a huge crater the Doctor feels the transmat rifle wrenched from his shoulder and drop. It lands on the edge of the crater. When he sees Dora's earrings detach from her ears and drop, and the sonic screwdriver threatening to go the same way, he realises that the power plant's magnetic core must now be below them. They struggle on to a steel door. The Air-Walker is leaping across the chasm behind them. The door is buckled and won't budge. The Doctor asks Dora if there is anything in the pockets of her suit that will help them. She finds a small pack of explosives. The Doctor uses half of this to blast the door open. They get through just as the Air-Walker leaps to kill them. There is a crackle of energy and when it lands with a thump beside them the creature is a smoldering corpse. They turn to see Zubedai lowering his rifle.

Xorax tries to explain to Amy why he has been taken prisoner but Amy soon grows bored and resumes her search for the TARDIS. She finds it on a shelf five metres up. Before she can reach it, Zarbotan enters the room on a silver hover-board. He glides down the aisles of shelves, about three metres off the ground. Amy scampers off to hide.

Zubedai raises his weapon to kill the Doctor but the Air-Walker's last act is to bite his ankle. Taking his chance, the Doctor throws the remaining explosives at Zubedai's feet and detonates it. All that remains is a crater. The Doctor and Dora run out onto a wasteland where they see some of the other prisoners being chased by three hunters. The hunters are deliberately missing their targets to herd them. This is halted when Harry and Rory begin to pelt the hunters with rocks from a hidden position inside the scoop of a derelict crane. The Doctor reaches the base of the crane and tells them to get down before the hunters get a lock onto their position. He spots an old electric buggy and sparks it into life with his screwdriver. The four of them climb aboard.

The three hunters are a stockbroker, a banker and a business manager. They are grumbling about the way the fugitives fought back when Krauzzen and his men arrive. Rather than sympathise, the gangsters use their weapons to blast the trio to ashes.

The Doctor has managed to drive about a mile to where the other prisoners are lying low. There is an emotional reunion for the Mossops (and thanks for Andrei for protecting their daughter) before everyone climbs onto the buggy. The Doctor drives it to a dome containing the abandoned rocket base. They find the control tower and climb up the rickety stairs. From an observation deck they see the next building along has an array of antennae on the roof. The Doctor guesses that if there is any power left on the moon it will be in that building. He finds the control tower's radio and is soon busy trying to repair it. When he has it working he tells them that all it needs is some power.

Amy plays a lengthy game of cat and mouse with Zarbotan until he finally corners her. He points his pistol at her and she closes her eyes. She hears a clunking noise and then opens her eyes to see Zarbotan has been replaced by Xorax (holding a blunt instrument). She asks where Zarbotan has gone and Xorax takes her to a crystal scope. Through it she sees Zarbotan tumbling through space to the atmosphere of Gorgoror. Xorax has disposed of him through a garbage chute.

Between them, the Doctor, Rory, Harry and Andrei concoct a makeshift zip-wire across to the roof of the nearby building. Andrei and the Doctor argue which of them should cross over to find the breaker switch that will give them the power. As they do so, Harry sails across the gap on the zip-wire. Krauzzen has him in his rifle's sites all the way but decides not to fire: he is interested to see what the prisoners come up with.

No sooner has Harry restored the power than Amy's voice is heard on the radio. She is in the TARDIS with Xorax. The Doctor gives her a crash course in how to fly down to rescue them. While he does that, Harry makes his way to the parapet of his building. The cheers his friends give him turn to gasps of horror when they see Krelbin emerge behind him. Krelbin raises a rifle and shoots Harry in the back. Harry vanishes in a blaze of light. The Doctor breaks off from a second call, this time to the LP9 police, to see Krelbin triumphantly holding up the scalp of the shologgi. He then starts to climb across the zip-line towards them.

Harry arrives in a holding cell in the LP9 police headquarters. Despite all that he can tell them, the police (and Zalu in particular) say that the politics are too complicated for them to do anything about the situation. Harry tells them that he was an Earth policeman and that politics were the bane of his life there, too. He says that he will stand up to Krauzzen in court and he will do anything to break the hold the gangsters have on Torodon. Again, his words fall on deaf ears until Xelos enters. She has heard from the Doctor on Gorgoror. Suddenly, Zalu makes up his mind. He tells Xelos to order up an Operational Response.

The TARDIS materialises on the observation deck and Amy bounds out, followed by Xorax. No sooner has Xorax shut the door behind him than Xaaael's raptor bird space ship arrives, hovering next to the tower with rapid-fire howitzers directed at the fugitives. Xaaael, wearing exoskeleton armour, gets out and strolls along the wing, followed by two gangsters armed with photon rifles. A ramp from the ship allows them to descend to the tower. Krelbin crawls over the parapet to join them. Krauzzen and his men arrive via the stairs.

Krelbin wonders where the other hunters are but the Doctor says that Krauzzen knows he is finished on the Outer Rim and is removing the evidence. Krelbin turns the transmat rifle on the gangsters but is immediately stabbed from behind by Zarbotan. The giant has glided up on his hover-board but he is in terrible condition. His real and artificial flesh have burned away to reveal a cybernetic skeleton and organic parts sealed in plastic containers.

The Doctor responds to the situation by challenging Krauzzer to a game for the ownership of the TARDIS, including an instruction manual for how to operate it. When the gang-boss declines, saying that he doesn't need to play for something he already owns, the Doctor asks the other gangsters if this is the sort of leader they want; someone too scared to play a game. This persuades Krauzzen to accept the Doctor's wager that he can make it back to the observation booth, chased by any two men that Krauzzen chooses, with a head start of five minutes. In order to out-psych the Doctor, Krauzzen offers him ten minutes. The Doctor sprints away and Krauzzen orders the prisoners and TARDIS to be taken to his ship, ready to leave orbit.

The Doctor decides to get underground to negate the speed of Zarbotan and Krauzzen's hover-plates. After a furious sprint through several buildings he arrives in a vast room full of barrels. Scrambling up these, he hears a photon rifle discharged and the barrels beneath him explode. He sees Krauzzen hovering up behind him and leaps to grab the hover-board. They veer wildly around the building as Krauzzen tries to shake him off. They collide with Zarbotan and knock him off his board. The giant full a hundred feet to the floor. The Doctor leaps onto some rubble and rolls away. He finds himself face to face with Zarbotan, now barely held together by his mechanisms. The Doctor races away until he finally reaches a large crater. He leaps over the lip and hides a few feet down. Krauzzen finds him easily but is perturbed to find his photon rifle ripped from his hands and his hover-board following it down the crater. He leaps off and hangs from a jutting timber beneath the Doctor. Krauzzen's mechanical parts pull down towards the magnetic core. Krauzzen's body rips apart and falls into the crater, leaving only an organic hand behind.

As the Doctor walks away from the crater he finds the giant Zarbotan waiting. Fortunately, his body has given out and he falls lifeless to the floor under the Doctor's touch.

The end of Krauzzen and Zarbotan is watched by everyone aboard Xaaael's Raptor Bird as it flies up to Krauzzen's ship. Xaaael feels that this makes him the leader of the gang. When Zalizta objects, Xaaael murders him in cold blood. The prisoners and gangsters disembark into the ship one by one. As they emerge from the airlock the gangsters are arrested by the armed police who are waiting for them. Zalu tells Xaaael that Xorax has agreed to testify against the gang.

Zalu asks if the prisoners had many casualties. Rory says that they lost one brave man; Harry Mossop. This is Harry's cue to emerge in Torodon police armour.