When someone tries to assassinate diplomat Sir Reginald Styles, UNIT investigate the possibility his attacker came from the future.

The Doctor forces the guerrillas to take him to the 22nd century where he is soon captured by the Controller.

The guerrillas infiltrate the Daleks' base to rescue the Doctor and Jo and ask them to return to their own time and alter history before the 20th century is plunged into a Third World War.

The Doctor and Jo arrive on the medieval planet Peladon, where the Doctor is mistaken for the Earth Delegate of the Galactic Federation and Jo is mistaken for a princess.

The Doctor is convinced the Ice Warriors are trying to sabotage the conference but his attempts to prove it see him accused of sacrilege.

The Doctor is sentenced to fight Grun to the death and his attempt to escape leads to an encounter with Aggedor.

Hepesh's plan has been exposed but he is still determined to prevent Peladon joining the Galactic Federation by leading a rebellion against the King.

The Doctor and Jo visit the Master at his island prison where the Doctor becomes curious about a number of ships sinking in the area.

The Doctor and Jo are trapped on the fort by a Sea Devil while the Master convinces Trenchard to help him steal some electronic components.

The Doctor is held prisoner by Trenchard while the Master attempts to contact the Sea Devils.

The Sea Devils attack the island prison and rescue the Master, prompting the Doctor to venture underwater to try and contact them.

The Doctor is taken to the Sea Devils' underwater colony where he tries to make peace with the creatures, only for the navy to attack the base.

The Sea Devils take over the naval base and the Doctor is forced to help the Master find a way to revive their colony.

The Doctor and Jo arrive on the planet Solos, on a assignment by the Time Lords, where they learn that the native Solonians are mutating into ant-like mutant creatures...

Ky transports himself and Jo down to Solos and the Marshal only agrees to help her if the Doctor assists Professor Jaeger in altering Solos' atmosphere.

The Doctor and Varan travel down to Solos to search for Jo and Ky but the Marshal orders his men to pursue them.

The Doctor and his friends are led to safety by Professor Sondergaard, who tries to help the Doctor translate the tablets.

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.

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.

UNIT are invited to observe a demonstration of the new TOMTIT machine, unaware its creator, Professor Thascales, is actually the Master.

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.

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 Master prepares to travel back to Atlantis but the Doctor links his TARDIS to the Master's to try and stop him.

Both TARDISes reach Atlantis, where the Doctor befriends King Dalios while the Master enlists the help of Queen Galleia to try and obtain the crystal of Kronos.

The Doctor enters the labyrinth to try and protect Jo from the minotaur but the Master has seized control of Atlantis and prepares to summon Kronos again.