An espionage ring is stealing secrets from the Government's top secret Cypher HQ, by posing as window cleaners.
The Doctor makes a return visit to Peladon some years after his previous visit. There he discovers that several miners have died and the ghost of Aggedor is to blame.
Chancellor Ortron accuses the Doctor and Sarah of being in league with the rebel miners and sentences them to be punished by Aggedor himself.
Desperate to avoid a revolt from the miners, the Doctor attempts to expose the fraud of Aggedor's ghost. Alpha Centauri has summoned Federation troops, but whose side are they on?
The Ice Warriors have taken control of Peladon. Pretending to cooperate, the Doctor concocts a plan to defeat the invaders.
