1 January 1977
David Garfield (Neeva), Victor Lucas (Andor) [1-2], Brendan Price (Tomas), Leslie Schofield (Calib), Colin Thomas (Sole) , Lloyd McGuire (Lugo) , Tom Kelly , Brett Forrest  (Guards), Rob Edwards [2-3], Pamela Salem , Anthony Frieze , Roy Herrick  (Xoanon)*, Leon Eagles (Jabel) [3-4], Mike Elles (Gentek) [3-4], Peter Baldock (Acolyte) .
|Written by||Chris Boucher|
|Directed by||Pennant Roberts|
|Produced by||Philip Hinchcliffe|
The TARDIS lands on a planet The Doctor doesn’t recognise – but its inhabitants seem to know him. They think he’s the Evil One and aren’t pleased to see him. Two warring tribes occupy the planet: the savage Sevateem and the reclusive Tesh, separated from each other by a deadly energy field. When the Sevateem believe their God, Xoanon, to be a captive of the Tesh, they decide to break through the barrier and rescue him. The Tesh, however, have other ideas.
Befriended by Leela, a Sevateem girl who dares to question the mighty Xoanon, The Doctor sets out to discover exactly what’s happening on this planet. Has he been here before? Is he responsible for the tribal wars? And can it possibly be that Xoanon, the mad God, is really The Doctor?
The Doctor, alone in the TARDIS, arrives on a mysterious jungle planet which he cannot resist exploring. He soon encounters Leela, a savage from the local tribe. She denounces him as the Evil One of her people’s fables. She has been exiled from her tribe, the Sevateem, for profaning their god, the mysterious Xoanon, who speaks to them through the tribe’s shaman, Neeva. Her father, tribal elder Sole, tried to protect her but died taking the Test of the Horda on her behalf. Now Leela is an outcast beyond the invisible barrier around her tribal home.
Neeva, meanwhile, has sent two men to murder her, an action witnessed by Leela’s friend Tomas. He kills one of them as Leela dispatches the other. In the jungle beyond, she encounters The Doctor, who soon wins her over by defending her from invisible monsters that rampage about, attracted by vibration of any kind. Exploring further, The Doctor finds a sophisticated sonic disruptor. It creates the force field that keeps creatures from attacking the village itself. Leela regales him with more folklore; the god Xoanon is kept prisoner by the Evil One and his followers, the Tesh, beyond a strange black wall.
The Sevateem have decided to launch an attack on the Tesh to free their god. They are led by the combative Andor, who is determined to free his god. He also believes an attack will unite the people. Andor suspects Neeva of being a false prophet, and Tomas tells him of Neeva’s attempted murder of Leela. Still, Andor believes the attack will succeed and is prepared to go ahead.
Two warriors are scouring the jungle when they find The Doctor. They also call him the Evil One and make a hand gesture which The Doctor interprets as the sequence for checking the seals on a Starfall Seven spacesuit. The warriors seize The Doctor but not Leela. They take him to the village council, where his face is shown to the tribe. Andor is convinced the prisoner is the Evil One and has him confined. However, Leela frees him using poisonous Janis thorns, which paralyse, then kill the victim. The Doctor is horrified by this. He instructs her, “No more Janis thorns, ever.”
The pair flees the village and heads to a clearing beyond, where The Doctor is greeted by a stunning sight. Carved into a mountain nearby is a relief of his own face.
The Doctor cannot recall clearly why his face is here. He persuades Leela to return to the village to learn more, despite their death sentences. They return to Neeva’s holy tent. The Doctor inspects the ancient tribal relics, recognising them as artefacts from an Earth survey expedition. He also finds a transceiver used by Neeva to hear the commands of Xoanon. It speaks with the Doctor’s own voice, exhilarated at hearing The Doctor, saying, “At last we are here. At last I shall be free of us.”
They head off to inspect the dark wall that stands at the entrance to the realm of the Evil One. The Doctor deduces it is a primitive time barrier. He is certain the Sevateem warriors will be massacred if they attack the fortress of their enemy, the Tesh. From afar they see the massacre unfold, as laser beams cut down warriors armed only with crossbows and other basic weapons. Half the tribe is lost in the assault.
One of the elders, the devious Calib, is first back at the camp, where he finds The Doctor and Leela. He is evidently intent on using The Doctor to break Neeva’s hold on the tribe by exposing the faith in Xoanon as mythology. Leela’s friend Tomas also arrives. He is apalled to find Calib has stabbed Leela with a Janis thorn to prevent her exposing his schemes. The Doctor gets Tomas to help him move Leela to Neeva’s tent, where he uses a bio-analyser to synthesise an antidote to the poison.
When the surviving warriors return, The Doctor, Leela and Tomas are invited to address the tribal elders in defence of their lives. Leela makes matters worse when she accuses Xoanon of causing the trap at the wall. Calib intervenes to suggest The Doctor is not the Evil One. He suggests this be proven by getting him to take the fabled Test of the Horda.
In the centre of the village is a pit full of Horda, two-foot-long worms which hunt in packs and react to the movements of their prey. They are reputed to strip flesh from a man in an instant. The Sevateem evolved the Test of the Horda as a trial of justice and bravery. It involves the defendant standing on a board over the pit, who then must shoot a rope attached to a boulder that is pulling the board out from under him.
The Doctor is given a crossbow. He must fire it at a precise moment to sever the rope without making him fall into the pit — the fate of the guilty. The Doctor succeeds, is proven a non-malign influence and freed. He proceeds to examine some relics of the tribe and repair a disruptor gun. He also tells some of the tribe that the Sevateem are the descendants of a “survey team” from a Starfall Seven Earth colony ship. The Doctor and Leela go to examine the face in the mountain; they climb into it by scaling The Doctor’s teeth.
Neeva returns to his tent, where the voice of Xoanon tells him the tribe will be destroyed. The mysterious being shuts down the sonic disruptor, leaving the village open to attack from the invisible beings. These descend on the village, killing indiscriminately and crushing Andor to death. Tomas uses the disruptor gun built by The Doctor to expose the true appearance of the invisible beings: ferocious, angry versions of the Doctor’s face.
Leela and the Doctor notice a figure in a spacesuit in the “mouth” entrance and follow it through a projection of a wall. Beyond this barrier is a rocket, which The Doctor recalls as belonging to the Mordee Expedition; his memory of events earlier in his incarnation are returning. Xoanon has detected The Doctor. When he reaches the ship, the god-creature is ecstatic that “we are here” and also maniacally pledging that “we must destroy us”.
The Doctor and Leela meet three of the Tesh who serve and worship Xoanon. They are human too, but technologically advanced and possessing telepathic abilities. The Doctor deduces both Sevateem and Tesh are descendants of the same crew from the Mordee Expedition, with the Tesh (or technicians) involved in the same deadly eugenics exercise as the Sevateem.
The invisible creatures which attacked the Sevateem are also part of the same deranged scheme. Xoanon is a highly sophisticated computer, designed to think independently. The Doctor repaired Xoanon but forgot to wipe his personality print from the data core, leaving the computer with a split personality.
The Doctor and Leela are soon imprisoned, then escape and find the device used to communicate with Neeva. The Doctor, speaking as Xoanon, instructs Neeva to tell Calib, who is now tribal leader, to lead the Sevateem survivors through the mouth of the carved face in the mountain. Calib accepts this instruction and leads them into the safety of the mouth, where the invisible beings cannot threaten the tribe.
With Leela keeping guard and holding the Tesh at bay with a disruptor gun, The Doctor ventures into the computer room of the ship to confront Xoanon. He blames himself for creating the computer’s maddened split personality. He now attempts to persuade it to shut down. Xoanon refuses and channels a vicious mental attack at The Doctor. As The Doctor writhes on the floor, Xoanon shouts in a child’s voice: “Who am I?”
Leela rescues The Doctor from the mental assault. As he recovers, he warns her of Xoanon’s power. Moments later they realise the computer has electrified the walls to kill them. The Tesh become more purposeful in tracking them down in the spaceship.
The Tesh also come under attack by Calib, Tomas and the survivors of the Sevateem, who reach the spaceship too. This diverts the Tesh while The Doctor and Leela return to the computer room. Xoanon briefly takes control of Leela’s mind, as he does of most of the Sevateem.
The Tesh and Sevateem soon converge on the computer room too and interrupt The Doctor as he tries to repair Xoanon. The computer has triggered the countdown to an atomic explosion. Elsewhere in the ship Neeva is alone and crazed, his faith in Xoanon shattered. The shaman uses the disruptor gun against one of the images of Xoanon/The Doctor projected through a wall. The ensuing blast kills Neeva but also interrupts Xoanon’s control of its subjects, allowing The Doctor to resume and complete his repairs. Xoanon’s circuits explode, knocking The Doctor out.
Two days later The Doctor wakes up to find himself aboard the spaceship in Leela’s care. She explains Xoanon has been quiet, and he interprets this as success for his extraction experiment. They visit the computer room and find Xoanon’s identity and sanity restored. The computer confirms it was running a eugenics experiment and thanks The Doctor for his repair work. The Doctor contacts the survivors of the Tesh and Sevateem to tell them Xoanon is cured and able to support their new society.
Unwilling to help them sort out the political question of which group should control the planet, The Doctor heads off to the TARDIS, followed by Leela. She insists on joining him on his travels. When The Doctor refuses, Leela runs past him and into the TARDIS. The Doctor follows Leela inside, telling her to come out. He is heard saying “Don’t touch that…!”, but it’s too late. Leela has started the dematerialisation process, and the TARDIS departs from the planet.