Ranjit, a small Indian boy, makes his way through a densely packed forest outside Calcutta. It is night and he is trying to find a place of safety, away from the sporadic violence in the city. He reaches a temple in a clearing where he intends to sleep. In the sky a light grows bigger. Ranjit realises that it is descending from the heavens, and with it comes a hideous shrieking. The light and noise overwhelm him and he passes ou t. When he comes to the light seems to be inside the temple. Creeping in to investigate he sees the glowing form of Shiva. Terrified, Ranjit flees.
In the TARDIS, Donna expresses a desire for curry. The Doctor sets the coordinates and lands in Calcutta. He thinks it is 1937. Confidently leading Donna through the alleyways he is oblivious to the debris and burned-out buildings. It is only when he arrives at the gutted remains of the eatery he was aiming at that he notices something is amiss. An old man informs him that it is 1947. The Doctor tells Donna that these are the last days of British India and that riots are sweeping the streets, particularly in Calcutta. Just then a mass of people stampede towards them. They are a charging mass, pursued by British troops on horseback. The Doctor and Donna are separated in the confusion and the Doctor finds himself plunging back into the melee to rescue an Indian doctor, Gopal, from beneath the hooves of a horse.
Meanwhile, at a makeshift camp some miles away, Edward Morgan is cursing Gopal’s failure to arrive for work. Morgan is a young doctor committed to helping all of the poor and sick that come to him. As more and more people arrive, mainly suffering from malnutrition, he finds himself working himself into exhaustion. His closest companion is a young English woman, Adelaide, who20looks up to him with respect. Morgan takes her to the third of three tents containing their patients. This one is reserved for people suffering from a new and terrible disease that not only disfigures them but turns them into aggressive psychopaths.
Cameron Campbell is the younger brother of Adelaide. He is fretting over the disappearance of Ranjit, bored that the troubles are keeping him confined to the house and starting, surprisingly he finds, to look forward to his family’s imminent return to England. A shower of stones at his window announces the sudden and welcome return of Ranjit who is keen to tell him about his adventure at the temple a week earlier. The boys rendezvous on the porch and make plans to visit the temple early the next morning but their conversation is interrupted when the family’s servant, Becharji, drives Ranjit off with a well aimed rock to the head. Cameron’s displeasure is forgotten when Major Daker arrives at the house, accompanied by the voluble Donna. She is particularly unhappy at losing the Doctor and being placed under virtual house-arrest for her own safety. She finds it difficult to fit in with the decorum and etiquette of the Campbell household and tries to explain her presence in Calcutta as a part of the hippy movement before realising that she is twenty years too early. To her relief a distraction is provided when a gigantic crocodile, disfigured by huge growths on20its body, attempts to attack the house. The implacable Major Daker steps into its path and shoots it dead.
The Doctor tries to take his leave of Gopal in order to find Donna. The Indian doctor, however, suggests that she may have been taken to the camp where he works. The Doctor accompanies him to the camp where he is shocked and saddened by the misery of the displaced Indians. Gopal tells him about the new disease that is bringing many new people into the camp. The Doctor is intrigued and makes for the isolation tent where these cases are kept. He uses psychic paper to introduce himself to Adelaide Campbell and Edward Morgan, claiming that he is Dr. John Smith of the Royal College of Surgeons, Rare and Tropical Diseases Unit. His sonic screwdriver tells him that the new illness is caused by cellular disruption, the result of Zytron energy which isn’t due to be discovered on Earth for three thousand years. He asks if there have been any strange lights in the sky. Adelaide says that there were some a week earlier and Gopal adds that a shooting star fell to the ground at the same time. Adelaide further divulges a rumour of ‘half-made men’ that are stealing people away. She says that one woman in the camp claims that her husband was stolen in just such a manner. The Doctor insists that Adelaide takes him to this woman. He soon learns that these men are white and featureless with no hair and only shadows for eyes. No sooner has he learned this than a ripple runs through the camp to greet the arrival of Mohandas ‘Mahatma’ Gandhi.
Gandhi is introduced to Adelaide and the Doctor who are both entranced by the small man’s history and personality. Gandhi is similarly taken with the Doctor and insists that they call him Mohandas. After a short philosophical debate they find Ranjit among them, desperate to talk. His head is bandaged after the attack at the Campbell residence but he ignores his injuries as he is more keen to tell Gandhi about his encounter with Shiva in the temple the previous week. The Doctor pronounces it his intention to visit the temple.
Major Daker returns to the British Army camp and is just sharing a whisky with Captain McMahon when shouting alerts them to trouble. They find a group of young privates huddled on the parade ground, claiming that two of their number have been kidnapped by white figures that arrived and vanished in a flash of light. Racing to the barracks to investigate, Daker and McMahon find that the ghosts have vanished. They separate to search the camp perimeter but McMahon is suddenly kidnapped by two ghostly assailants. One of them vanishes in a silvery shimmer with the soldier just as Daker is running to his help. The second turns towards Daker who shoots it several=2 0times, causing it to vanish too.
When Ranjit hasn’t appeared for the appointed meeting at five o’clock, Cameron decides to set out for the temple alone. He rides part of the way on his bicycle and is perturbed that nobody is about as he would have expected on a normal day. He is held up by a puncture but goes on by foot. He is terrified by a thirty foot cobra, oddly misshapen like the crocodile, but drives it off with his catapult.
Donna wakes in the Campbell house and descends for breakfast wearing one of Adelaide’s dresses. She makes an ally in Ronny, the oldest Campbell sibling. Adelaide returns full of news about her tough but interesting night at the camp. She is amazed when Donna says she is looking for the Doctor because he is one of the things she wants to talk about. Donna races off to the camp just as the Doctor (along with Ranjit, Gopal and Gandhi) are setting off for the temple on four elephants. After a stormy greeting Donna joins their expedition. They near the temple and discover Cameron being held at bay by a pack of over-large monkeys. The Doctor drives them away with a firework from his pocket.
At the temple the Doctor forbids the boys to enter but goes in with Donna, Gandhi and the great man8 0s attendant. Inside the temple they all see something different: Donna sees the Racnoss, the attendant sees Shiva, Gandhi sees darkness descending on the world and the Doctor sees it for what it is, a disguised space ship. He uses the sonic screwdriver to disable the cloaking technology but the spaceship immediately vanishes. On the way back to the camp the Doctor explains that they had seen a glamour in use, a psychic shield that shows itself as whatever the viewer is most afraid of. To Donna’s amazement, Gandhi accepts all of this futuristic technology at face value. Back at the camp the Doctor announces his intention to return to the TARDIS to seek out the source of the Zytron energy, which is the unstable energy that is mutating all of the life in the area. However, when he sets about calibrating his machinery he notices that his screwdriver is missing.
No sooner has Cameron’s disappearance been noted in the Campbell household than Major Daker arrives. He adds the boy’s apparent kidnapping to that of his three men the night before and asks Sir Edward’s permission to search the city. Sir Edward agrees.
Ranjit has seen another boy in the camp with the screwdriver. The boy says that the Doctor dropped it while getting off an elephant and then runs off into a field with Ranjit in pursuit. As they fight for p ossession of the instrument the boy activates the control. Two of the white men promptly appear in the field. Ranjit escapes but the men grab the other boy and vanish.
Donna and Gandhi return Cameron to his home where the Indian has an appointment with the boy’s father.
Major Daker leads a party of soldiers through the poorest parts of Calcutta. The Major is growing steadily more angry with each house that they search. He sees the denials of the occupants of any knowledge about the missing Britons as lies. He eventually works himself up into such a state that he threatens one family with his revolver. When one of his men, Wilkins, intervenes the Major turns his gun on his own man but the remainder of the group of soldiers speak up. They all reason with Daker who eventually fires a shot into the air and promptly collapses. His cap falls off, revealing the black growths around his head that are the effects of Zytron poisoning.
The Doctor emerges from the TARDIS with his timey-wimey detector, adjusted to locate the sonic screwdriver. It leads him on a frantic dash through the back streets until his progress is halted by a large man with a huge club. This man has all the enlargements and growths associated with Zytron poisoning as well as a psycho tic desire to murder the Doctor. Just when he seems about to succeed, and the timey-wimey detector is smashed, he is shot dead by Wilkins. The Doctor is saddened by this loss of life, as is Wilkins who has never killed before. The Doctor strides off in pursuit of alien technology.
Donna is in the garden taking tiffin with Mary, Adelaide and Cameron Campbell. Adelaide is telling Donna about her work at the camp while Mary voices her disapproval, saying that the Indians are not grateful for the help they receive which raises Donna’s ire. Just as a full scale argument seems about to erupt, Ranjit arrives with the sonic screwdriver, followed by Gopal. To Mary’s distaste Donna invites them to sit down and explain where Ranjit found the device. Inside the house Gandhi’s discussion with Sir Edgar is not going well. It has reached a cultural impasse when the Doctor bursts in. He tells Sir Edgar that there is a major threat to the safety of the population and that he needs Sir Edgar’s help galvanizing all available forces to search the area for the source of the dangerous energy. When Sir Edgar rejects this out of hand, dismissing the Doctor as a crank, Gandhi offers to put all his followers at the Time Lord’s disposal. Seeing Donna through the French windows, the Doctor steps onto the lawn. Ranjit returns the screwdriver to the Doctor and tells him how he rescued it from two ‘half-made men’. The Doctor suspects that someone has put a trace on the device and immediately turns it on. Four white men appear in the garden, surround him, then all of them vanish with the Doctor.
The Doctor arrives at his destination full of anger. He has recognized his captors as gelem warriors, cannon fodder from the War of Five Hundred Worlds. They are remorseless and durable troops, siphoned off from captured races to make machine creatures fashioned from pseudo flesh. Five living creatures have died to make each unthinking warrior. He is marched through a cave system into a vast spaceship, the product of many apparently incompatible technologies. The Doctor is impressed with the mind that could fuse so many disparate parts into an operable machine, but appalled by the potential disaster it signifies. Eventually he is led to the weed-like alien at the heart of the ship. This creature introduces itself as a Jal Kalath, Darac-Poul-Caparrel-Jal-7 (Darac-7). When the Doctor accuses him of being a criminal who is poisoning Calcutta Darac-7 denies it. He says that the real culprit is Veec-9 who is on Earth using stolen glamour technology and stealing humans to male gelem warriors. Darac-7 is only there to find him and take him back to the eleven Hives of Jal Paloor for trail. He claims to have been chasing Veec-9 for four centuries, hence the patched up and degraded state of his ship. However, he says Veec-9’s ship is=2 0in worse condition, and is the source of the poison. He adds that his quarry intends to harvest fifty thousand humans to make an army of ten thousand warriors. The Doctor suggests that he leave the tracing of the renegade to him, the TARDIS has better technology for seeing through the glamour technology.
The Doctor suddenly reappears in the Campbell’s garden and tells Donna they have to return to the TARDIS. They march through the back streets o the TARDIS but arrive just in time to see it being taken by gelem warriors. The Doctor uses his sonic screwdriver to reveal that a tracking device has been disguised as a fly buzzing around Donna’s head to lead the alien force to the TARDIS. They walk away from the scene only to find Gopal waiting at the next corner, pointing a gun at them.
Adelaide returns to the camp for work. In the early evening gelem warriors appear and begin to snatch people at random, vanishing with their captives and reappearing almost immediately. Edward Morgan and Adelaide are both taken, along with dozens of Indians. Ranjit evades the warriors by hiding. After the attack ends he finds Gandhi and persuades him to go with him in search of the Doctor.
Gopal’s gun is a Mezon disintegrator 7.5, revealing him as Veec-9 . Gopal accuses the Doctor of being in league with Darac-7 who he says is a bounty hunter and opportunist mercenary. Cameron appears from nowhere and uses his catapult to shoot the gun from Gopal’s hand. The Doctor picks up the weapon. Gopal begs the Doctor to kill him. He says he is being persecuted for speaking out against the tyranny of the Hive Council on his home world and is hiding on Earth. Darac-7 has traced him and is using his time on Earth to build an army of warriors that he can sell back to his government. The Doctor suggests that they retire to Gopal’s apartment for a cup of tea and a chance to discuss events. There, the Doctor explains that Darac-7 let him go from the spaceship as a ruse to capture the TARDIS. He needs to find the holding area where thousands of captives can be stored until a Hive transport ship arrives and he thinks it must be under the hills near Darac-7’s ship. They are interrupted by the arrival, in the street outside, of Ranjit and Gandhi who are leading a large group of followers. They had come to Gopal’s residence in search of news of the Doctor and are delighted to find him already there. They bring news of the attack on the camp.
The Campbell residence comes under attack and Sir Edgar, his wife Mary and son Ronny are among the next to be kidnapped by the warriors. They find themselves in a cavern with hundreds of other people, fenced in by a glowing wall of energy.
The Doctor asks Gopal how he moves between his home and his ship. Gopal produces a transmat pod which the Doctor brings to life with his screwdriver. This immediately causes a group of gelem to appear in the room. With a tweak of the controls the Doctor disables them all, claiming that he has not killed them as they were never, technically, alive. The Doctor opens the chest of one of the lifeless forms and extracts a matter relocator. He adjusts it slightly so that it lands them near, not in, the holding area. Donna, Gopal, Gandhi, Ranjit and Cameron form a human chain holding onto the Doctor as he activates the device. They arrive on a steep slope in a rocky range of hills. They make their way up to a cave entrance and down a dark tunnel. The Doctor has to drive away three enlarged scorpions that bar the way and then they reach a solid wall. Using his sonic the Doctor transforms the wall into the door of the spaceship. It is decided that the Doctor, Gandhi and Ranjit will enter the craft while the others use the screwdriver to find and free the prisoners.
Donna leads them down the tunnels until they arrive at the cavern containing the prisoners. Using setting 59-A on the screwdriver, as the Doctor has instructed, she breaks down the energy barrier. The Campbells joyfully greet C ameron while the other prisoners flee into the tunnels. Gopal uses his transmat device to kill the gelem warriors who try to stop them.
Ranjit thinks that they might have to kill the alien bounty hunter but Gandhi suggests that violence is never the solution. The Doctor agrees and says he wants to try to find a peaceful solution. They enter the central chamber and notice the TARDIS. The Doctor begins by ordering Darac-7 to leave with his dirty Zytron energy. The Jal Karath responds by producing warriors who take them prisoner and push Gandhi into the extraction machine. The old man simply acquiesces. However, rather than being killed his presence inside the machine causes it to explode. The Doctor announces that the machine was designed to take the badness out of people, but there was no badness in Gandhi. There is a knock-on effect from the explosion as systems begin to fail all round them. They escape into the TARDIS as the ship explodes.
Donna gathers Gopal, the Campbells and their servant Becharji as well as Edward Morgan. Together they form a vast chain with those prisoners too sick or injured to flee from the cavern. Using the transmat pod she takes them out into the open air. They find themselves on the slopes as the first of the other freed captives pour from the cave entrance. They are at a loss as to what to do. It i s dark and they are lost in a vast landscape, miles from Calcutta.
The Doctor takes the TARDIS to the sick bay of the British army camp. He sees that Major Daker has fully recovered and asks him if he can mount a major rescue operation. Then he returns the TARDIS to Donna and her crowd of escapees and ushers them all inside. He transports them back to Morgan’s camp and heads to the isolation tent. There he observes that the Zytron patients are on the mend. Before he left the imploding spaceship he rigged an energy inversion programme so that the ship would suck back its dangerous particles as it was destroyed. With a final farewell to Gandhi, the Doctor and Donna return to the TARDIS and prepare to leave. He informs Donna that Gandhi is in the last months of his life and is due to be assassinated early the following year. Donna is saddened by this and remarks that Gandhi reminds her a lot of the Doctor, who replies that he could never be as forgiving as Gandhi.