In search of the Doctor, an antimatter creature attacks UNIT and the Doctor is forced to send an SOS to his people, the Time Lords, but they have troubles of their own.
Following the advice of the First Doctor, the Third Doctor and Jo have crossed through the black hole to the strange, desolate world of antimatter.
The Doctors are trapped in the universe of antimatter. There they confront the creator of the world – Omega, a legendary figure from Time Lord history, long believed dead.
Omega intends to escape his antimatter world and needs the Doctors to take his place. But they discover the terrible truth about Omega and realise that he can never escape.
The Doctor and Jo arrive in 1926 on the cargo ship SS Bernice. But when the TARDIS is taken by a huge hand and a dinosaur appears, the Doctor suspects that all is not as it seems.
The Doctor and Jo have been miniaturised and trapped inside a Miniscope, the property of showman Vorg. The Scope has been impounded on the planet Inter Minor and may be destroyed.
The Drashigs are pursuing Jo and the Doctor through the Miniscope. On Inter Minor, scheming bureaucrats intend to release the Drashigs in a plan to topple their leader.
The Doctor is desperate to save the lives of Jo and everyone trapped inside the Miniscope, but is hindered by the Inter Minorans who have their own agenda.
Captain Mike Yates is taken over by the super computer, BOSS, and ordered to kill the Doctor. Cliff and Jo are trapped by the maggots as UNIT launch their attack.
Cliff is dying and the maggots are on the verge of transforming into giant flying insects. Time is running out for the Doctor as BOSS launches its plan for world domination.
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.
Neither the humans or the Draconians are willing to believe the Doctor and Jo's story that someone is deliberately attempting to provoke a war between Earth and Draconia.
Accused of being a spy, the Doctor is sentenced to imprisonment on the Moon while Jo is taken into the custody of an old enemy.
The Doctor and Jo are the Master's prisoners. In a bid to escape, the Doctor makes a dangerous spacewalk.
On Draconia, the Doctor reveals the Master's plan to provoke war to the Draconian Emperor. But the Master escapes, taking Jo as a hostage.
The Doctor leads a mission to the Ogron home world to apprehend the Master and rescue Jo. But the Master is in league with some old enemies of the Doctor.
Injured by the Orgrons, the Doctor asks the Time Lords to send the TARDIS after the Daleks. Leaving him to sleep and recuperate, Jo goes to explore the planet Spirodon.
The Doctor recovers from his coma and befriends a Thal expedition but is captured by the Daleks and taken to their base. Then a second Thal expedition arrives with terrible news...
In the Dalek city, the Doctor breaks out of his prison cell and joins forces with the Thals. With the Daleks in pursuit, he is forced to improvise a daring escape plan.
The Doctor and the Thals escape from the Dalek city and the Doctor is delighted to find Jo is alive. But the Daleks are preparing deadly bacteria to kill all life on the planet.