The planet Jenggel once fought a devastating war with Earth, but that war is now long past and Jenggel is now a popular vacation spot. One of the attractions is the unspoiled wilderness of the island Papul, which is now ruled by the Indoni, natives of the islands Batu and Javee. The Papul now make a living any way they can under the brutal Indoni rule; some act as tour guides, showing Indoni and human tourists their own native villages. One such party arrives in the village of Akima to see its sacred Mumi, the mummified body of a village chieftain -- but the Mumi quivers to life and spits poisonous snakes from its mouth. Only one tourist survives, and the Mumi speaks to the villagers, telling them to reclaim what they have lost.

The TARDIS materializes on Batu, where the Doctor and Victoria look for a quiet establishment while Jamie entertains himself in a bar with scantily clad native women. He hits it off with a beautiful Indoni girl named Wina, and nearly gets into a bar fight with a human named Pan when he sees Pan abusing his Indoni girlfriend, Santi. Pan, almost amused by Jamie’s presumption, decides that he’s bored of Santi and goes home with another woman, Kety, whom he picks up at the bar. Santi doesn’t realize what a narrow escape she’s had, for when Pan bores of Kety he shoots her dead. He’s a mercenary for hire, one of a team of psychotic killers called the Dogs of War; only the one named Clown has a hint of morality about him, and even for him it’s mainly an intellectual curiosity. When Pan rejoins the others the next morning they tell him that they have a commission from the corrupt Indoni President, Sabit. Sabit insists that the deaths at Akima village were caused by Papul guerrillas rather than by the supernatural, but it’s all the same to Pan, as long as he gets to kill.

The Doctor and Victoria meet Wemus, a charming young Papul who offers to take them on a tour. Intrigued, the Doctor accepts the offer. Jamie then arrives with Wina, and as she and Victoria size each other up, Santi arrives, furious with Jamie for driving off her “boyfriend”. Seeing a chance to show Wina up, Victoria suggests that Santi join the tour as well, and largely to irritate Wina, Santi accepts. The Indoni businessmen Ussman and Budi join the tour, as does a smarmy human tourist named Drew. As they approach Papul on a motor canoe, Santi recalls the stories of the island’s cannibal tribes -- but it’s too late to turn back now.

In retaliation for the Mumi attack, the Dogs of War descend upon Akima village, burn the Mumi, execute the villagers and burn the village to the ground. There are mass executions in the town of Jayapul, and all hints of insurrection are dealt with brutally and immediately. Sabit carefully controls the release of information to the outside world; if he has his way, he will be seen as a man bringing peace and civilisation to the Papul, and nobody need know that his agents in fact staged many of the attacks themselves in order to give him an excuse to crack down on the native population. But dark forces are at work elsewhere; in the village of Agat, the Christian missionary Father Pieter is waiting anxiously for the return of his friend Father Tomas when the village suddenly goes mad around him. Pieter’s trusted friend Julius hears the skulls in the museum speaking to him, and the normally peaceful and friendly Papul in Agat cast away thirty years of missionary teachings almost immediately, brutally butchering the Indoni businessmen in their village as Pieter watches in horror...

Wemus leads his tour deeper into the jungle, narrating their journey while quietly considering the attractive Wina and Santi. The tour is interrupted when his friend Kepennis, the guide who led the tourists to Akima, arrives and tells him of what happened; he fears that the Indoni will blame the Papul for the attack, and that nowhere on the island will be safe. However, as they talk, Victoria wanders a short distance away and is captured by a patrol of Indoni who refuse to let her return to her friends, claiming that it’s too dangerous. By the time the Doctor realizes that she’s gone, it’s too late. The Doctor stops Jamie from rushing off into the jungle in search of her, and they continue to Akima, hoping that they can find help there. Instead, they find the village in flames. Kepennis rescues the Mumi from the flames, and the Doctor studies the body and finds that it’s infested with a strange purple fungus.

The other tourists want to return home immediately, but the decision is taken out of their hands when Papul guerrillas emerge from the jungle and capture them all. The guerrillas’ leader, Tigus, fights for Operaki Papul Gallaki, and he sees the tourists as enemies, even regarding Wemus and Kepennis as collaborators. On the orders of the OPG leader, the Krallik, they are to be held as hostages with which the OPG can negotiate Papul’s freedom. Ussman, however, knows that Sabit will never abandon Papul’s rich mineral resources and tourist attractiveness for the sake of a few ordinary people; the hostages are thus as good as dead.

Indoni military patrols begin to escort tourists in Papul, and when another Mumi comes to life in the village of Jikora, the Indoni burn the village to the ground -- and place the tourists under arrest. Sabit doesn’t want word of these events getting out, and he thus sends out a press release claiming that the tourists were killed by rebels and allows the soldiers at the outpost in Wameen to “entertain” themselves. The tourists are all dead by the time Victoria arrives, but her treatment is very different. Agus, the officer in charge of the patrol that caught her, seems charming enough, and he insists that most of the Papul support the Indoni’s attempts to bring civilisation to their island. Agus shows Victoria the rusting remains of military vehicles on the beach, proof that the Indoni fought to protect the Papul during the war with Earth. Victoria is unsure what to believe.

The Doctor tries to speak reasonably with Tigus and urges him to seek a peaceful resolution to the conflict, but Tigus insists that only violence will get the Papul’s point across. The discussion halts when they find a shuttle which has crashed in the jungle, brought down by a Snatcher which has devoured its crew. Only the Indoni pilots, who was strapped into his seat, has survived, but he dies of his injuries as Tigus questions him. Tigus does learn that his brother is being held prisoner in Wameen, and orders his men to split up; half will continue taking the prisoners to the OPG base in the southern swamps, while the others go to Wameen to rescue his brother. Jamie has shown some sympathy for the Papul cause -- as a Jacobite, he identifies with their desire to rid their country of foreign occupation -- and Tigus therefore orders him to go to Wameen and help his men fight; if he refuses, the Doctor will be killed. The Doctor advises him to go, especially as Victoria may have been taken to Wameen as well.

Victoria grows bored and decides to explore the village, but on her way out of the fort she hears a whimpering sound from a dark alcove, and investigates to find a Papul prisoner being tortured by a grotesque man with cybernetic implants. Agus catches her as she flees, and this time, locks her up; he insists that the prisoner is a multiple murderer, but Victoria now knows that the Indoni are no better than the Papul. Elsewhere on the island, Papul are reverting to the ways of cannibalism, killing the Indoni businessmen who have patronised them for years; and the Dogs of War are travelling from village to village, questioning the Papul about the Krallik and killing them when they refuse to answer. Clown has dressed himself in full clown makeup, complete with jester’s hat, to underline the madness of it all; and Pan is losing his mind, remembering the night in the tattoo parlour on Earth where he lost his temper with the artist while showing off his new tattoo to the one woman he’d ever loved...

At the OPG base in the swamps, a young guerrilla named Wayun returns to find his brother Tumal’s head on a spike. Tumal had objected to the OPG’s brutality, and the Krallik ordered his death. The shock clears Wayun’s head, and he finally realizes that the Krallik is evil and unnatural. The other guerrilla are ashamed of what they’ve done and frightened of the look in Wayun’s eyes, and they do nothing to stop him as he enters the darkened hut. There, he sees a hunched figure on a throne, flanked by two others. As he steps forward, the figure speaks to him, claiming that war is carnage and slaughter and obscenity, and that there is no other way. As Wayun steps forward to kill the Krallik, he sees his leader’s face for the first time...

The Doctor learns more from Tigus about the Krallik, who founded the OPG after Indoni soldiers raped and murdered his wife and children. Ever since then he’s lived in the swamps, and allows no one to see him, cultivating an air of mystery and fear both amongst the Indoni and the Papul who follow him. As the group continues through the jungle, trying and often failing to avoid the many predators, they approach Tigus’ home village -- but the Dogs of War have visited it, and the village is burning, all of Tigus’ friends and family slaughtered. In his rage he pulls a machete on the Doctor, and when Budi tries to flee in panic, Tigus chases him down and severs his head with repeated machete blows. Even he is sickened by what he’s done when he calms down, but he claims that it’s the Indoni who have turned him into this monster. His prisoners are horrified by what they’ve seen, and Kepennis has fainted dead away.

Father Pieter tries to slip quietly out of Agat, but is caught by Julius, who presents him with a handful of purple fungus. The Papul have been eating this delicacy in recent months, but Pieter suspected that the fungus could cause progressive brain damage, and he realizes that it may be responsible for the atrocities he’s witnessed. This knowledge doesn’t save him; Julius ties him to a chair, presents him with the severed head of Father Tomas, and forces Pieter to eat. Later, the Dogs of War put in at the village of Jayapul for the night, but as the other Dogs terrify the cowed villagers, Clown continues on alone to Agat. Pieter had been keeping a journal of Indoni atrocities and sending word to galactic rights organizations, and Sabit wants him dead. However, Clown finds the village deserted; the Indoni have been butchered and the Papul have returned to the jungle. Pieter is still alive, but has been driven mad by what he’s seen and done, and Clown, who has no love for missionaries, decides not even to put him out of his misery.

Jamie and the OPG guerrillas attack the Indoni outpost at Wameen, where they find surprisingly few soldiers waiting for them. They are too late to save Tigus’ brother, who has been tortured to death, like the tourists from Jikora. They are also too late to rescue Victoria, who has been taken into the jungle by Agus to see the OPG’s brutality for herself. Disappointed, they return to Tigus’ group, and resume the journey to the southern swamps. The final part of the journey must be by river, through dangerous territory controlled by the Kirowai, a tribe of cannibals. During the journey the rebels’ canoes are attacked by the beasts which live in the river, and one of the canoes is overturned. Drew manages to swim to the other canoe, while Ussman makes his way to one shore and Jamie and Santi reach the opposite shore. Tigus refuses to return for them, and the Doctor has no choice but to continue on, now separated from both of his companions. Wemus comforts Wina for the loss of their friends, and as the two grow closer Kepennis grows more irritated, telling his friend that it’s wrong to feel compassion or love for the Indoni after what they’ve done.

Santi wants to get to the coast, but Jamie insists upon following the river and rejoining the Doctor. The decision is taken out of their hands when they are captured by Kirowai, who force their captives up into their tree-hut village. There, they see that the cannibals have already cooked and are eating Ussman. Santi can translate some of the Kirowai dialect, and the chief, amused by her fiery spirit, decides to make her his tenth wife -- and to kill and eat Jamie at the wedding feast. Jamie, desperate, asks Santi to translate for him; if the chief allows him to live, Jamie will help the Kirowai to get rid of the strangers who have trespassed on their lands, and to capture their leader, a man of great spirit and courage -- attributes which the Kirowai prize in their “food”.

Victoria can’t forget the brutality she saw in the Indoni fort, but Agus remains charming and friendly towards her, insisting that she will soon see for herself that the OPG are much worse. Instead, he and his men are caught by surprise and gunned down by the Dogs of War, who impale Agus and his men on spikes before Victoria’s eyes, intending to blame the OPG. Clown has gone AWOL, overwhelmed by the violence and madness, and without him the Dogs’ brutality is going entirely unchecked. The Dogs keep Victoria alive, however, as Sabit intends to “rescue” her friends -- and then hold them hostage to ensure that she reports his version of events to the Earth Alliance, so he can continue his oppressive policies without opposition. The Dogs take off again, with Victoria their captive, as Pan continues to flash back to the tattoo parlour, where he lost his temper and killed the tattoo artist. His lover realized that he really was a psychotic killer after all, and, realizing that he’d lost her forever, he killed her too.

Tigus’ party reaches the home of the Krallik, where the Doctor sees that Papul are also being killed by the man who claims he’s freeing them. While Drew takes advantage of their arrival to answer a call of nature -- or so he claims -- the Doctor studies sacks of the purple fungus which he found in the Mumi in Akima. The OPG has been selling the fungus as a delicacy to fun their activities, and Tigus allows the Doctor to sample some. The Doctor analyses the fungus he’s tasted and, to Kepennis’ amazement, immediately identifies a mix of muscle stimulants, depressants, and other neurochemicals which leave those who eat the fungus open to telepathic suggestion and telekinetic stimulation. The voice of the Krallik then speaks in Tigus’ mind, ordering him to let the Doctor face him personally...

The Doctor reluctantly enters the Krallik’s chamber to find Wayun’s body on the floor and two Mumis sitting on either side of the Krallik -- a patchwork body with the head of a missionary and the hands of a prostitute sewed to the torso of an Indoni merchant, a symbol of all that is destroying Papul. The Doctor realizes that this monster was never truly alive in the first place, which means that that the real Krallik is elsewhere. When he hid out in the swamps he ate the purple fungus to survive, and it’s given him the power to communicate telepathically with anyone else who eats it. By packing the Mumis with the fungus, the Krallik was able to stimulate their long-dead muscles into movement; he must also have fitted the hollow corpses with speakers and catapults in order to make them talk and spit snakes. But the fungus is a parasite which has been feeding on his cortex as he eats it, and it’s driven him quite mad, twisting his dreams of freedom into a nightmare of carnage and butchery.

The Dogs of War finally receive the signal they’ve been waiting for, and storm the OPG fort, gunning down the unprepared guerrillas. The survivors fight back, and in the ensuing battle most of the Dogs are killed, as is Tigus. Drew reveals to his fellow prisoners that he’s been working with the Dogs all along; he went undercover as a tourist so the OPG would capture him and take him to the Krallik, and once he got here he sent a signal to the Dogs. However, Pan has never really liked Drew, and he shoots him dead before continuing to the Krallik’s chamber. There, he decapitates the Krallik, but one of the Mumi guardians spits a poisonous snake at him, and he dies remembering the lover he killed -- his sister.

The Doctor reveals that the “Krallik” is also controlled by the fungus, and orders Kepennis to drop the charade. Kepennis has been too passionate about the destruction of his homeland and Wemus’ attraction to the Indoni Wina, and he got to the Mumi in Akima first so he could remove the evidence of his tampering with it. Kepennis “fainted” when Budi was murdered because Wayun attacked the Krallik at the same time, and Kepennis was concentrating on animating the Krallik to defend itself. Kepennis admits that the Doctor is correct, but insists that the Indoni must be made to pay for what they’ve done; as the Doctor had feared, the fungus has driven him mad.

When Wemus refuses to leave Wina’s side, Kepennis triggers one of the Mumis, which spits snakes at Wina, killing her. Kepennis also turns the Krallik’s decapitated body on the others, but Wemus gives his life to attack it and chop it to pieces. Jamie and the Kirowai then attack the fort, and in the ensuing confusion, the Doctor turns his own mental powers on Kepennis, taking advantage of the small amount of fungus he’d just eaten. Although Kepennis has eaten more of the fungus than anyone else, the Doctor’s mind is stronger, and he forces Kepennis to look into himself and see his heart of darkness. The horror leaves Kepennis incapable even of moving by himself, and the Kirowai take him away with them, per their agreement with Jamie. The Doctor is distressed that it didn’t occur to him to try this before Wina and Wemus were killed. He, Jamie, Victoria and Santi then set off back to Batu; the Doctor hopes that Santi will spread word of what the fungus does, and prevent any further such atrocities. Perhaps he’s hoping too much of her, however.