The Krotons

The TARDIS materialises on a rocky mountainside in a desolate part of an unknown planet. On leaving the TARDIS The Doctor, Jamie McCrimmon and Zoe Heriot spot a city below and decide to go and visit it. As they approach the outskirts of the city they come across a metal door in a rock face. Suddenly the door opens and a man appears. He looks dazed and drained of energy. Before they can go to his assistance nozzles on either side of the doorway spray a smoke at the man and he is vaporised.

The Doctor and his companions rush to the city and enter a hall. They arrive in what appears to be in the middle of a ceremony. After a woman called Vana goes through a doorway a council leader comes over to see the newcomers. Selris explains that they have arrived in the city of the Gonds. When they tell him that they have just seen a man vaporised Selris disbelieves them – especially when he realises that this happened in what the Gonds call the Wasteland. The Doctor has correctly deduced that the man they had seen being killed earlier had been a Gond who had gone through the doorway before Vana and that Vana must therefore be about to suffer the same fate. Another Gond, Thara who is is Selris' son, overhears their story and agrees to enter the wasteland with them so as to save Vana. They arrive back at the door just in time. The Doctor jams the nozzles with rock just as Vara emerges. The Doctor grabs her and they take the catatonic girl to Selris' home to recover.

It is then that The Doctor and his companions learn that the brightest of the Gonds are selected and, like generations before them, they enter the machine of the Krotons so as to serve the Gond’s masters. However, once they enter the machine they are never seen again. It is revealed that this has been happening for thousand of years – after the Krotons descended on the planet in their spaceship that they call a Dynatrope. Since that day the Gonds have lived by the Krotons' laws with each child taught by the Kroton's learning machines. The Krotons are in fact currently in suspended animation, awaiting a time when they can be reconstituted by absorption of mental energy. Hence why they have been educating the Gonds and then summoning the two most brilliant students and then draining them of their mental energy before disposing of them in the Wasteland – that the Krotons created by releasing a poison when, in the past, the Gonds had tried to fight back.

Taking A Stroll

The Gonds had seen the Krotons as friends up to now, but they now realise that they are in fact slaves to the Krotons. After a futile attack on the Kroton's learning machines by a group of Gonds, which results in a snake-like tentacle emerging from the Krotons’ machine, Zoe decides to try out one of the learning machines. She finds it extremely simple and so passes a test with flying colours. To her horror she is then selected to join the Krotons. On learning what Zoe has done, and that she must now enter the Krotons’ machine, The Doctor also takes the test. He too is selected to enter the Kroton’s machine.

Inside they are initially drained of energy – but the soon recover. They then come across a tank of liquid in which crystals are beginning to form into bulky looking shapes. The Doctor takes a sample of the liquid before they both head for the exit. The Doctor then takes the liquid sample back to the TARDIS where he finds that it is based on tellurium – a crystalline substance. They then return to the Gonds city so as to locate their chief scientist. On realising that the Krotons are a crystalline race The Doctor has an idea on how to defeat the Krotons.

Investigating The Kroton's Machine

Back inside the Dynatrope the reanimated Krotons have realised that The Doctor and Zoe are too clever to be Gonds and that they must therefore be recaptured to help them power their ship. Meanwhile Jamie has been attempting to break into their ship so as to rescue his friends. The Krotons allow Jamie in and then force him to tell them about the TARDIS and make plans to destroy it. They then declare him to be a primitive and therefore he is of no further use to them – but Jamie has other ideas. The Krotons then try to destroy the TARDIS but, to the frustration of the Krotons, The Doctor’s time machine simply re-appears further up the mountain due to the fact that The Doctor remembered to set the HADS (Hostile Action Displacement System).

With some of the Gonds preparing to attack the Krotons another Gond, called Eelek, plots to seize control of the council from Selris by leading the uprising. Selris persuades the Gonds to forgo a frontal assault on the Krotons and instead they try to remove one of the giant pillars which support the Dynatrope. This though results in the roof of the under hall to collapse killing several Gonds.

The Doctor, with the help of Selris requests that the Gonds' scientist make some sulphuric acid. It is then, along with Zoe, that they learn that Jamie is inside the Dynatrope and they head back to the Wasteland exit to find him – there they discover Jamie trapped halfway under the door and so help him out.

The Doctor and the Metal Snake

On returning to the Gonds’ city The Doctor and Zoe discover that the Krotons have ordered that they must re-enter their ship. To persuade the Gonds to comply they have promised to leave the planet if they are given the two travellers. In the absence of Selris – who is assisting Beta, the Gonds scientist, to produce the sulphuric acid - Eelek has agreed and so The Doctor and Zoe are forced to re-enter the Dynatrope. Luckily Selris, who knows how important it is to get the acid to The Doctor, arrives in the hall just in time to throw himself through the closing door. Before the Krotons kill him Selris is able to give The Doctor the container containing the acid.

The Krotons then reveal that they need The Doctor and Zoe's mental abilities to replace two of their crew members who 'ceased to exist' during a space battle that caused them to land on the Gond's planet. While The Doctor keeps the Krotons talking Zoe is able to pour the acid into the Krotons' liquid tank causing the Kroton to suddenly collapse and begin to dissolve. The Doctor notices that the Dynatrope is dissolving too and once outside they find that Jamie, Beta, Thara and Vana have been pouring acid onto the outside of the ship.

With the Krotons destroyed, The Doctor, Jamie and Zoe slip away, leaving the Gonds to find a new leader and to decide their own destiny.