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

Jo uses the guerrillas' time machine to travel to the 22nd century where the Controller tricks her into telling the Daleks where she's come from.

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.

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.

The Doctor and Jo land on a spaceship in the far future as it is attacked by Ogrons, which the human crew see as Draconians. The Doctor and Jo are taken to Earth as spies.

The Doctor and Jo are taken to Earth, where both humans and Draconians believe them to be a spy for the other side.

The Doctor is sentenced to life imprisonment at a lunar penal colony while Jo encounters an old enemy.

The Master rescues the Doctor from the lunar penal colony, aiming to take him and Jo to the Ogrons' planet, and the Doctor's attempt to escape leaves him stranded in space.

The Doctor, Jo and the Master are taken to Draconia, where the Doctor tries to convince the Draconians of the truth.

The Doctor, Williams and the Draconian Prince head to the Ogrons' planet to find evidence of the Master's actions but the Master tricks Jo into leading them into a trap.