The Doctor and Sarah are drawn into the Mandragora Helix, an entity which exists among the stars and which transports the TARDIS to 15th century Italy.

The Doctor rushes to rescue Sarah from the Brethren of Demnos while Mandragora tries to bring them under its control.

The Doctor saves Giuliano from Federico's men, then they try to find Sarah, unaware Hieronymous has hypnotised her to kill the Doctor.

With Mandragora having taken complete control of the brethren, the Doctor tries to find a way to drain off the Mandragora's energy on Earth before it wipes out the guests at Giuliano's masque.

The Doctor and Sarah arrive in a quarry during blasting operations and when Sarah is buried under rubble, she discovers a stone hand.

The Doctor and Carter attempt to gain the trust of the Nunton staff before Sarah takes the hand into the reactor.

Eldrad uses the energy from the reactor to regenerate herself and tries to force the Doctor and Sarah to take her back to Kastria.

The Doctor and Sarah attempt to get Eldrad to the regeneration chamber but Rokon has left traps in their path.

A mysterious evil is at work on Gallifrey. The President of the Time Lords has been assassinated and the Doctor caught red-handed. An inexorable master plan has been set in motion. There can be no escape.

The Doctor is arrested for the President's murder and struggles to avoid his immediate execution.

The Doctor battles the assassin inside the matrix dreamscape, while the Master tries to bring about his death in the real world.

The Doctor realizes the Master is planning to tap into the Time Lords' power source to extend his own life, an act that will destroy all of Gallifrey.

Travelling alone, the Doctor lands on a nameless planet in the far future where he meets a warrior woman named Leela, recently banished from her tribe, the Sevateem who recognise the Doctor as the "Evil One" and wish to destroy him.

Despite protestations against being the Evil One, mounting evidence points to the Doctor's prior involvement with Leela's people, and an error in judgment he once made in their distant past that puts them all in immediate jeopardy.

Venturing into the mouth of the giant statue, the Doctor and Leela meet the Sevateem's rivals, the Tesh. The Tesh greet the Doctor as a lord but his attempt to save Leela's life causes them to view him as an enemy.

As the Saveteem and Tesh finally close in for a fight to the death, the powerful but long-suffering Xoanon ignores their strife to commit its full resources toward killing the Doctor, even to the extent of destroying everyone.

The Tardis materializes aboard a mining ship on a desert planet, inhabited by a human crew and their robot servants. While Leela adjusts to life travelling with the Doctor, one of the ship's robots mysteriously kills a member of the crew.

As the strangulations continue and the humans aren't sure who to blame, Leela meets up with an anomaly among the robot crew - an inquisitive, supposedly mute single-function labor robot capable of independent reasoning. Meanwhile the Doctor starts looking into the possibility that the murderer is a robot, and another crew member is targeted for death.

Hearing about a man who grew up only around robots and who has threatened to start a robot revolution, and who may be aboard the sandminer under an assumed name, the Doctor takes D.84 to seek out a possible secret workshop where he would be restructuring robot programming. Meanwhile, as one crew member suffers a complete mental breakdown, reprogrammed robots are order...

With secrecy no longer necessary for the robot revolution, Controller Taren Capel shuts down all friendly robots and gives the remaining humans an ultimatum, or else their deaths will be slow and painful. With no conventional weaponry aboard their commercial vessel, the humans do what they can to resist while giving the Doctor time to work out a permanent solution.

The Doctor and Leela land in Victorian London, and find themselves in the middle of missing girls, mutilated bodies, and vicious Chinese gangs. The Palace theater, presenting hypnotist Li H'sen Chang seems to be at the center of it all.

After escaping from the vicious giant rat in the sewers, the Doctor & Leela team up with Litefoot. Chang, Mr Sin and Weng-Chiang go in search of the time cabinet, while the Doctor and Jago go in search of Chiang's lair.

Leela follows Chang in order to find Greel's hideout while the Doctor and Litefoot set about finding her.

Having rescued Leela from the jaws of the giant vicious rat, she & the Doctor dress up and attend Chang's show at the palace, but end up as part of the act. At home, Litefoot tries to protect the time cabinet.

Weng-Chiang has stolen the time cabinet from Litefoot's house, so the Doctor and Leela go to try and stop him from using it. They find an opium-drugged Chang. Jago teams up with Litefoot for their own investigation.

The real face of Weng-Chiang is revealed as the Doctor, Leela, Jago and Litefoot face their final battle against both Magnus Greel and a trigger-happy Mr Sin.