Written by: Brian Hayles
Directed by: Lennie Mayne
Returning to the planet Peladon fifty years after his previous visit, the Doctor finds King Peladon's daughter Thalira on the throne, and the planet once again on the brink of conflict with the Galactic Federation. The Queen's chancellor, Ortron, is mistrustful of the Federation's mining operation on Peladon to obtain the valued mineral trisilicate. The miners, second-class citizens on Peladon, are on the point of uprising, and Federation representatives Alpha Centauri and Engineer Eckersley are struggling to keep the peace.
According to reports, a ghostly figure of Peldon's sacred beast Aggedor has been responsible for deaths in the mine, and the Doctor must use all of his wits to keep the miners from full-scale insurrection while calming the paranoid xenophobia of Ortron.
Eventually, the Doctor uncovers that the deaths have been due to the machinations of Eckersley, in league with a renegade group of Ice Warriors hoping to obtain the trisilicate for themselves and sell them to Galaxy 5, who are at war with the Federation. Eckersley has been using a matter transmitter combined with a heat ray to make it seem as if the statue of Aggedor is killing miners.
While the Ice Warriors take ruthless control of the planet, the Doctor and the miners manage to mouth a counter-attack, taking control of the matter transmitter and heat ray and turning it against Eckersley and the Ice Warriors.
After the Ice Warriors are defeated, Eckersley takes the Queen hostage, but he is killed by the real Aggedor, though the beast sadly dies in the process.
In the end, with peace restored, Galaxy 5 surrenders and the Doctor and Sarah head on their way in the TARDIS.