The enigmatic Doctor, afraid that schoolteachers Ian Chesterton and Barbara Wright will reveal his secrets to the people of 20th century Earth, has taken them and his granddaughter Susan back to the dawn of human history. There, the four travellers are dragged into the savage politics of a tribe of cavemen who have lost the secret of making fire…

Prisoners of the earliest humans, the TARDIS crew are caught in a deadly power play for leadership of the tribe.

The TARDIS crew must make fire for the early humans to stay alive. But once they do, they may not be allowed to leave!

The TARDIS arrives on the planet Dulkis where the Doctor, Zoe and Jamie decide to have a quiet holiday. Only to find the Evil Dominators and their robotic slaves, The Quarks have arrived on a radioactive island, where they plan to detonate a bomb in the planet's core, which will turn the entire planet as source of radioactive fuel for their invasion fleet.

The Doctor and Jamie are captured by the Dominators, who subject them to an intelligence test, while Zoe and Cully attempt to convince the Dulcian council of the threat.

Zoe and Cully are captured by the Dominators and put to work alongside the survey team while the Doctor and Jamie decide to return to the island to help.

The Doctor and Zoe are interrogated by Rago, who is planning to present his terms to the Dulcian council, while Jamie and Cully try to find a way to strike back against the Quarks.

Jamie and Cully manage to rescue the Doctor's party and together they try to find a way to stop the Dominators before they destroy the entire planet.

The Doctor and Liz are summoned to the Wenley Moor Research Centre by the Brigadier, after several staff members suffer nervous breakdowns.

The Doctor attempts to convince people there are monsters in the caves, prompting Major Baker to start shooting at a reptile man.

The Silurians contact Quinn for help in retrieving the creature while the Doctor and the Brigadier organise a search of the moors.

With Quinn dead, the Brigadier decides to take an armed party into the caves, prompting the Doctor to contact the Silurians himself.

Worried about the Old Silurian's growing friendship with the Doctor, the Young Silurian has the scientist infect Baker with a virus and then release him.

While the Doctor and Liz try to find a cure to the virus spread by Baker, the Young Silurian kills the Old Silurian and takes control of his people.

While Liz distributes the cure to the virus, the Doctor discovers the Silurians now plan to wipe out humanity by destroying the Van Allen Belt.

The storm-lashed planet Karn. Near a graveyard of crashed starships, the demented surgeon Solon hides in his castle, the last acolyte of the Time Lord despot Morbius. He only needs one final item to make his master live again... and then the Doctor and Sarah arrive...

The Doctor is captured by the Sisterhood, and Sarah Jane is blinded freeing him. The Doctor has no choice but to go back for a cure, unaware that he is leaving Sarah Jane in the hands of a treacherous Dr. Solon and the renegade Time Lord Morbius.

While the Doctor goes to confront the Sisterhood to seek a cure for Sarah Jane's blindness, Solon realizes that he must transfer Morbius' brain into a new body before it is too late.

Morbius lives once more, but as a rampaging beast. The Doctor is forced to ally with Dr. Solon to bring him to heel, but the two disagree about what should happen to Morbius.

The Doctor and Sarah arrive in Renaissance Italy unaware that they have brought a deadly alien energy force with them.

The Mandragora energy joins forces with the secret Brotherhood of Demnos. Count Federico plots to steal the Dukedom of San Martino from his nephew, Giuliano.

Tempted by the promises of ultimate power offered by Mandragora, Hieronymous plots to eliminate the threat posed by the Doctor and uses an unwitting Sarah as his weapon.

As the leading scholars of the era assemble in the palace for the masque, Mandragora prepares to attack, intent on sending the world into a new dark age.

Deep space, 5000AD. An Earth supply shuttle is infected by a strange sentient space-borne virus, which quickly spreads to the crew of the refuelling station on the moon Titan. Even worse, the Doctor himself falls victim. But why is Leela immune, and what is the virus's ultimate goal?

Leela and Lowe take the Doctor to the Bi-Al Foundation for help. But how can they cure an infection of the mind?

Miniaturised clones of the Doctor and Leela are injected into his brain. But they must now fight the virus on its own level. And its servants are closing in around them.

The Nucleus, now grown to human size, is determined to spawn and take over the Galaxy. Only the Doctor and Leela can stop it.