The Master prepares to travel back to Atlantis but the Doctor links his TARDIS to the Master's to try and stop him.
The Master enlists the help of Krasis to control Kronos while Yates tries to bring the TARDIS to the institute only to come under attack from dangers from the past.
The Doctor realises the Master is trying to harness the power of Kronos, last of the Chronovores, but is unaware Percival is harbouring him at the institute.
When Joan decides to make herself more attractive to her husband Eddie, she little realises that it will start off a chain of events which will bring the uneasy truth between them and Barbie and Bill into open warfare.
UNIT are invited to observe a demonstration of the new TOMTIT machine, unaware its creator, Professor Thascales, is actually the Master.
Despite the fact that Eddie is a staunch socialist and Bill is a true blue Conservative, there are many subjects on which they both agree. For instance, they are both against discrimination. When Bill tells Eddie that he was once refused a drink in a pub because of his colour, Eddie's British sense of justice and fair play is outraged and he sets out to prove that the opposite must be the case, with rather painful results.
The Doctor is forced to help the Marshal cover up his actions with the Investigator but Jo and the others attempt to escape to expose him.
There comes a time in every husband's life when he is tempted to stray from the marital home: and Eddie and Bill are no exception - for the seven year itch has no colour bar. However, the trouble with an itch is that one is tempted to scratch it.
The Marshal's premature use of Jaeger's experiment is threatening to destroy Solos' atmosphere and the Doctor returns to Skybase to try and correct the damage.
An industrial dispute between Eddie and Bill at the factory causes a domestic dispute with their respective wives, Joan and Barbie. However, blood is thicker than water - as Eddie learns to his cost.
Callan substitutes himself for an assassin in order to prevent an assassination.
The Doctor and his friends are led to safety by Professor Sondergaard, who tries to help the Doctor translate the tablets.
Eddie decides that Maple Terrace just isn't big enough to hold both the Booths and the Reynolds. But when he tries to organise a petition to "keep Maple Terrace white", his plans misfire - with hilarious results.
Callan and Lonley break into a courier's house to find out how he's operating.
The Doctor and Varan travel down to Solos to search for Jo and Ky but the Marshal orders his men to pursue them.