The Doctor in the Jungle

The Doctor is still travelling alone when the TARDIS materialises on a mysterious jungle planet. On exiting the TARDIS he cannot resist exploring his new surroundings. It is not long before he encounters Leela, a female savage from a local tribe, who, on seeing The Doctor, denounces him as the Evil One.

On questioning Leela, The Doctor discovers that she has been exiled from her tribe, the Sevateem, for profaning their god, the mysterious Xoanon, which speaks to them through the tribe's shaman, Neeva. The Doctor soon wins Leela over by defending her from the invisible monsters that rampage about, attracted by vibrations of any kind. Exploring further, The Doctor finds a sophisticated sonic disruptor which creates the forcefield that keeps the creatures from attacking the village itself. As The Doctor explores Leela regales him with more folklore of her people: the god Xoanon is kept prisoner by the Evil One and his followers, the Tesh, beyond a strange black wall - a deadly energy barrier which separates the Sevateem from the forbidden land beyond, which is controlled and enjoyed by the Tesh.

The Sevateem meanwhile are planning to launch an attack on the domain of the Tesh to free their god. They are led by the combative Andor, who is determined to free his god, and also believes that an attack will unite the people. He also believes that Neeva is a false prophet. Meanwhile two Sevateem warriors, while scouring the jungle, find The Doctor and they too call him the Evil One, making a protective hand gesture which The Doctor interprets as the sequence for checking the seals on a Starfall Seven spacesuit. The warriors then seize The Doctor and take him to face the village council who decide to hold him captive. Leela, who had been ignored by the warriors when The Doctor was captured, manages to free him by using poisonous Janis thorns to kill his guards. This act of savagery horrifies The Doctor but despite this when they are spotted the pair are forced to flee the village. They soon arrive in a clearing where The Doctor is greeted with a stunning sight: carved into a nearby mountain is an impression of his own face. More worryingly is The Doctor can not recall how his face could have got there.

The Tribe of the Sevateem

So that he can solve this mystery The Doctor persuades Leela to return to the village with him, despite the death sentence that has been placed upon them. In Neeva's holy tent and The Doctor inspects the ancient tribal relics that are kept there. He recognises them as artefacts from an Earth survey expedition. He also finds a transceiver used by Neeva to hear the commands of Xoanon. The Doctor is shocked to discover that Xoanon speaks with The Doctor's own voice.

The Doctor then decides to take a look at the dark wall that stands at the entrance to the realm of the Evil One. On arriving there The Doctor deduces it is a primitive time barrier and is convinced the Sevateem warriors will be massacred if they attack the fortress of their enemy, the Tesh. However, they are helpless to witness from, a distance, a massacre unfold, as laser beams cut down the Sevateem warriors who are armed only with crossbows and other basic tribal weapons. Unable to help The Doctor and Leela return to the village but when they are discovered, by one of the returning warriors, Leela is stabbed with a Janis thorn. The Doctor though is able to use one of the artefacts, a bio-analyzer, to synthesise an antidote to the poison.

Leela and Calib

When the remaining warriors, who survived the massacre at the barrier, return to the village The Doctor tries to convince them that he is not a threat to them. But his attempts are hampered by Leela when she accuses Xoanon of causing the trap at the time barrier. So as to prove he is not the Evil One, The Doctor agrees to take the fabled Test of the Horda which involves being suspended on a rope above a pit which contains two-foot-long worms, the Horda, who are reputed to strip flesh from a man in an instant. The Doctor then has to fire a crossbow to sever the rope without falling into the pit - which of course The Doctor succeeds in doing, and is therefore announced as being a non-malign influence and freed.

The Doctor and Leela then head for the mountain that has his face carved on it. Meanwhile Neeva returns to his tent, where the voice of Xoanon tells him that the tribe will be destroyed. The sonic disruptor, controlling the barrier around the village, suddenly shuts down leaving the village open to attack from the invisible beings who descend on the village, killing indiscriminately. But when Tomas, one of the Sevateem, uses a disruptor gun, that The Doctor had earlier repaired, to expose the true appearance of the invisible beings: they are revealed to be ferocious, angry depictions of The Doctor's own face.

Back at the mountain The Doctor and Leela spot a person in a space suit in the ‘mouth’ of the stone image of his face. They then witness the strange person walk through a projection of a wall. They follow him through and discover a passage carved out of the cliff beyond which is a rocket. Unknown to them both, Xoanon has detected The Doctor and Leela arrival, and when The Doctor reaches the rocket the god-creature becomes even more ecstatic. The Doctor and Leela are then greeted by three representatives of the Tesh, who confirm that they serve and worship Xoanon. Even though they are human, like the Sevateem, The Doctor realises that they are more technologically advanced and possess telepathic abilities.

Leela a Warrior of the Tribe of the Sevateem

The Doctor then discovers that Xoanon is a super-computer, which arrived on the planet when a spaceship crashed there many years ago. The Sevateem and Tesh are therefore descendants of the crew who were originally to have surveyed the world for possible colonisation. The Doctor also realises that he has met the crew before in an earlier visit where he helped the technicians repair their computer. Unfortunately he neglected to erase his own personality print which resulted in it having a split personality – so making it schizophrenic. This caused the computer to split the crew up - the technicians (Tesh) on the one side and Survey Team 6 (Sevateem) on the other – as an experiment The Tesh were raised as ascetic telepaths who would tend with religious fervour to its every need, while the Sevateem descended into savagery.

The Doctor then learns about the manifestations attacking the Sevateem’s village and so uses the remote communications device to instruct the remaining Sevateem to leave the village. He then tells them that the tribe will be safe from the invisible beings once they have entered the mouth of the carved face in the mountain. With Leela keeping guard and holding the Tesh at bay with a disruptor gun, The Doctor, realising his earlier mistake, ventures into the computer room of the spaceship to confront Xoanon and to persuade it to shut down. But instead the super-computer carries out a vicious mental assault at The Doctor, causing him to collapse. As The Doctor writhes on the floor Leela rescues him from the mental assault. At the same time the Sevateem arrive and start to attack the Tesh. This diverts the Tesh allowing The Doctor and Leela return to the computer room but Xoanon briefly takes control of Leela's mind. The Doctor also realises that Xoanon has triggered a countdown to an atomic explosion.

Elsewhere in the spaceship Neeva is alone but crazed, his faith in Xoanon shattered, and when he sees one of the images of Xoanon/The Doctor projected through a wall he fires a disruptor gun at it. The ensuing blast kills Neeva but it also interrupts Xoanon's control of its subjects, allowing The Doctor to wipe the additional personalities from the computer. But at the same time Xoanon's circuits explode, knocking The Doctor out.

Two days later The Doctor wakes up to find himself aboard the spaceship in the care of Leela. They visit the computer room and find Xoanon's identity and sanity restored. The Doctor then contacts the survivors of the Tesh and Sevateem and tells them Xoanon is now cured and able to support their new society. The Doctor then returns to the TARDIS only to find Leela waiting for him. Having decided that she no longer wants to stay on her own planet she asks him to allow her to join him on his travels. When he refuses Leela darts into the TARDIS ahead of him and refuses to come out. The Doctor is therefore forced to follow her in. As he does so the dematerialisation process starts. It seems The Doctor has gained a new companion.