Alpha Centauri

The TARDIS returns to the planet Peladon about fifty years after The Doctor’s last visit there with his then companion Jo Grant. The Doctor, with his latest companion Sarah Jane Smith is about to discover that things have changed. The planet is unsettled due to a war between the Federation and Galaxy 5. Peladon is rich in the mineral trisilicate, which is needed for the war, but the Pel miners are refusing to operate the new equipment brought in by the Federation. Queen Thalira and her High Priest Ortron are trying to convince them that the equipment is safe. It appears that the spirit of Aggedor is working against them as his image has appeared and several miners have been killed. The latest victim is the alien mining expert Vega Nexos, when he and engineer Eckersley, demonstrate a new sonic lance to speed up the mining process. Gebek, who represents the miners, is open minded about the technology, but another miner, Ettis, wants to use force to return Peladon to the old ways.

The Doctor and Sarah are captured but luckily Alpha Centauri is still on Peladon in an ambassadorial capacity and vouches for The Doctor. Ettis and a group of miners try and break into the planet's armoury but cannot get through the doors which are electronically controlled from the communications room. Ettis sends Preba to try and get them open but he is captured. This action discredits Gebek and Ortron orders Gebek and Preba executed. The Doctor helps them to escape and persuades Queen Thalira that Gebek is her only chance of peace with the miners. He goes with Blor, the Queen's champion, to check the cave where the spirit of Aggedor last appeared. Ettis uses the sonic lance to trap The Doctor and Blor inside. The image of Aggedor appears and Blor is killed.

When Gebek realises what Ettis has done, he rescues The Doctor as Aggedor appears once more. Sarah, on hearing a message in the communications room, goes to find The Doctor in the caves. However, she gets lost and finds herself by the new Federation refinery. She sees someone moving inside but is then knocked unconscious by the automatic defence system. Luckily Eckersley sees her, via a monitor in the communications room, and goes to help her.

Alpha Centauri with Eckersley

The Doctor wants the miners to wait and to work normally while he investigates the situation. Gebek agrees, but when they have gone, Ettis plans another attack on the armoury. However, when Gebek is arrested The Doctor helps him to escape. Ortron proposes that the rebellion must be crushed and that The Doctor must be captured and executed. Meanwhile Ettis goes to the communications room, where he gets Alpha Centauri to open the armoury door. He then leaves, taking Sarah hostage. Sarah manages to escape but is soon captured by Ortron, who accuses her of conspiring to overthrow the Queen. When The Doctor arrives to try and make Ortron see sense, the High Priest condemns them both to be punished by Aggedor. The guard captain tells Eckersley and Alpha Centauri that Sarah has been captured by Ortron and they try and get Queen Thalira to intervene. Queen Thalira goes to talk to Ortron but she arrives too late to save The Doctor and Sarah as they have already been placed into a pit under the temple.

In the pit, The Doctor manages to calm Aggedor with a spinning pendant and demands that he and Sarah be released. Queen Thalira then orders Ortron to comply. The Doctor again tells the Queen to talk to Gebek and she asks him to arrange a meeting. Ortron, however, orders The Doctor not to leave the Citadel. When he tries to do so, the High Priest has him arrested and thrown in a dungeon leaving Sarah to deliver Queen Thalira's message to Gebek instead.

Sarah in Trouble

Sarah and Gebek then go to see Queen Thalira and learn that Alpha Centauri has followed a suggestion, made by Eckersley, and has summoned Federation troops to provide support. Sarah reasons that the troops will leave if all seems normal and Ortron manages to persuade the miners to go along with this. Alpha Centauri then receives a message from the Federation troops who it seems are already in orbit and so will arrive shortly. Gebek frees The Doctor from the dungeon and they go to investigate the refinery, following Sarah's assertion that she saw someone in there. The Doctor opens the door and they are shocked when they are confronted by an Ice Warrior.

The Ice Lord Commander Azaxyr arrives and states that the planet is under martial law. He wants the miners to work under threat of death and takes hostages who will be killed every hour until the miners are working again. He also threatens that the planet will be destroyed unless trisilicate is being delivered. Azaxyr then has the Ice Warrior, Sskel, take The Doctor, Sarah, Eckersley and Alpha Centauri to the communications room. Azaxyr agrees to allow The Doctor to try and persuade Gebek to get the miners working again and Sarah realises that it was Sskel that she saw in the refinery and so these are not the troops that Alpha Centauri thought were being summoned. The Doctor goes to talk with Gebek to get the miners to pretend to co-operate to give him time to deal with the Ice Warriors. He then raises the temperature in the mines so as to dull the Ice Warriors' senses which will allow the miners to attack them.

When the miners attack the Ice Warriors, The Doctor learns from Rima about Ettis' plan, to destroy the citadel using a sonic lance that he has pointed there, and goes to try and stop him. However, Azaxyr has set the lance to self destruct, and watches on a monitor as The Doctor and Ettis fight. Ettis activates the lance and it explodes, apparently killing The Doctor and Ettis. The Doctor is not dead, however, and, when he recovers he goes to find Gebek. They then both head for the refinery.

Queen Thalira Counseled by Ortron

Azaxyr switches off the heat in the mines and cuts off the air supply instead, which is controlled from the refinery. Ortron is killed and Queen Thalira is held prisoner as an escape is attempted from the throne room. Alpha Centauri and Sarah manage to get to the communications room where Alpha Centauri sends an SOS message. Sarah sees Azaxyr and Eckersley talking in the refinery, on the monitor screen, and discovers that they have been working together in a plot to supply trisilicate to Galaxy 5. She also discovers that Eckersley has a statue of Aggedor which he is moving round the mines using a matter projector linked to a directional heat ray to kill the miners.

Outside the refinery, The Doctor also overhears Azaxyr and Eckersley and Sarah sees him on the monitor. Relieved that The Doctor survived the explosion Sarah goes to join him and her appearance outside the refinery allows Gebek to knock out the guarding Ice Warrior. Azaxyr, who has returned to the communications room, sends Sskel to stop The Doctor getting into the refinery. The Ice Warrior arrives too late and starts to burn through the refinery door, but The Doctor uses the Aggedor statue to stop him. Seeing that Aggedor is now on their side, the miners attack the Ice Warriors. Eckersley however, uses the defence system to try and stop The Doctor and The Doctor is apparently killed once more. The miners then storm the throne room where Azaxyr is holding Queen Thalira hostage. They struggle and Azaxyr kills Sskel by accident. The Ice Lord is then fatally stabbed by one of the Queen's guards.

Having lost control Eckersley kidnaps Queen Thalira and makes his escape by dragging her through the tunnels towards his space shuttle on the other side of the mountain. Thinking once again that The Doctor has been killed Sarah goes to the refinery where she finds that The Doctor is not dead - he had put himself in a coma when the defence system became too much to cope with. On learning that Eckersley has kidnapped Queen Thalira, The Doctor uses the real Aggedor to track Eckersley down. When they catch up with him Aggedor attacks Eckersley but he kills the beast before he is himself killed.

With the crisis over Queen Thalira asks The Doctor to stay on as advisor, but The Doctor instead suggests Gebek for the role. Alpha Centauri reports that the war with Galaxy 5 is over and they are keen to negotiate peace now that they realise that their supplies of trisilicate are not going to be arriving. Gebek reports that the TARDIS has been found so enabling The Doctor and Sarah to leave.