Guiliano attends the death bed of his father; his uncle, Count Federico arrives just as his brother gasps his last. It is clear there no love between the two family members, Federico would wish to govern San Martino with an iron fist, Guiliano is a gentler man. However, as Guiliano stands between him and ruling San Martino, Federico must find a way to usurp his nephew. Perhaps he too, should die as his father did? And perhaps it too should be seen in the stars by the court's seer, Hieronymous? Hieronymous is reluctant to twist his readings of the stars to give the portents of doom as asked, but knows that he cannot stand up against Federico. Inwardly, he believes that there is power in the stars and that one day he will be granted access to that power.

The Doctor and Sarah are wandering around the corridors of the TARDIS when they find the secondary control room. The Doctor states that he can operate the TARDIS from there just as effectively. However, the TARDIS is caught by the Mandragora Helix and drawn into the centre. Taking a quick look around the Doctor and Sarah narrowly avoid an encounter with some Helix energy and they quickly return to the TARDIS and leave. Arriving in Italy during the 15th century, the Doctor surmises that the Helix energy has pushed the TARDIS off course. When Sarah is snatched by a group of monks, the Doctor tries his best to rescue her. The Doctor discovers that some of the Helix energy has travelled with them to Earth. Now he must warn the local population. Unfortunately, his next encounter is with men loyal to Count Federico...

Observers in a dome on the freezing surface of a dying world monitor a spaceship. As their power fades, they realise that they might be unable to obliterate the ship when it reachs the opitmal range for destruction. There appears to be no choice, but to obliterate the ship early and hope that nothing survives...

The Doctor and Sarah emerge from the TARDIS on what could be Earth. They soon realise that they are in a quarry just as a detonation is about to be triggered. They dash for shelter as the explosives are detonated. Men from the quarry dash down and find the Doctor quickly enough. It is not long before they locate Sarah, buried under a pile of rocks. When she is freed, Sarah is found to be holding on to a stone hand. Both Sarah and the Doctor are taken to a local hospital. Sarah appears to be suffering mild concussion, but it is the rigidity of her hand that raises some concern. A study of the hand she was found holding raises some other concerns. It appears to be millions of years old - from a time before humans walked the Earth - the hand is quite humanoid. It is silicon-based and a sample form the hand is absorbing radiation from around it.

When Sarah awakens, she leaves the hospital, avoiding the Doctor and sets off for a nearby nuclear reactor complex. There, she enters one of the rooms adjoining one of the reactors and sits with the stone hand. The missing finger on the hand grows back and the hand begins to move...and Sarah's thoughts are dominated by the one thought, "Eldrad must live!"

In response to a summons from the Time Lords, the Doctor is returning to Gallifrey. Suddenly he has a vision of Time Lords milling about in the Panopticon, a gun being raised, a shot is fired and the President falls to the ground. Horrified by this, the Doctor realises he must warn the Time Lords. On arrival, however, guards surround the TARDIS and the Doctor realises he will be caught up in all kinds of procedures and interrogations - there is no time to lose. He leavs a warning note and at the first chance, slips past the guards.

A guard spots the Doctor but a shot kills the guard, leaving the Doctor with the likelihood of more questioning. Once again, he eludes the other guards and returns to the TARDIS, a move remarked upon as predictable by a watching figure. With the Doctor's note and a dead guard, Castellan Spandrell launches a full hunt: and all steps must be taken to protect the President.

As the events in the vision begin to draw closer, the Doctor realises that he is being set up to take the fall. The question is, who is the real assassin and how can he be drawn out into the open?

At a meeting of the tribe of the Sevateem, Leela is informed that for blaspheming against Xoanan she is to be banished. The alternative is to take the test of the Horta. Her father agrees to the test, something which Leela tries to prevent, pleading for forgiveness. A scream from another part of the village signals the end of the test...and Leela's father. Her banishment commences, but Neeva, spiritual leader of the tribe does not appear to be convinced that this is sufficient as she send two warriors after her.

In the forest, some way from the village, the TARDIS materialises. Struggling to remember something, the Doctor sets off to explore. He encounters Leela who calls him the Evil One. However, the main concern appears to be invisible monsters crashing through the forest, creatures that belong to the Evil One. Distracting one of the monsters, the Doctor decides that he needs more information...and when he is captured by members of the tribe he finds himself faced with more questions. The tribe also recognise him as the Evil One. They demand that he release Xoanan, their god. Around the village, the Doctor spots artefacts that once belonged to some Earth expedition. Have the tribe always lived there or are they more closely connected to the expedition than at might first appear? The answers to this and more might lie beyond the Wall, into which is carved the face of the Evil One...the Doctor!

A small group of people live and work on board a sandminer: storms on the surface cause valuable minerals to gust around and the miner collects them. Vast fortunes can be made, if the mining is carried out correctly or if the head of the operation has a good instinct for the best storms. Commander Uvanov prides himself on being one of the best. His fellow miners are a mixture of people, some of them are even members of the founding families, having fallen on hard times they have chosen to take a tour on a sandminer to restore their fortunes. Apart from chasing storms there is little to do aboard the sand miners, menial tasks are performed by the robots. The main robot is a super-voc class robot, SV7. Next in line are the voc-class robots, the V series, and then there are the low grade dum-class, the D series. All robots are programmed to serve humans and would cause no harm, so when a government appointed weather surveyor is found murdered Uvanov can only conclude that one of them is the killer. Until two strangers are found in one of the scoops. The Doctor and Leela state their innocence, but perhaps the most ridiculous statement the Doctor makes is that perhaps the killer is one of the robots.

As murder and sabotage befall the crew of the sandminer the unthinkable seems to be true - that the robots are killing the humans...

London towards the end of the 19th century: its streets are the stalking ground of a mystery killer; women are disappearing; there is talk of Jack the Ripper returning; one taxi driver, Mr Buller, confronts the magician, Li H'Sen Chang, at the Palace Theatre. His wife has never been the same after she had been to see Chang's magic show, and last night she came to the theatre and has not been seen since. Threatening to go the police, Mr Buller leaves. As he walks the streets figures steal out of the dark and kill him. Despite their attempts to intervene, the Doctor and Leela cannot help the man but do succeed in capturing one of the killers. It later transpires that he is a member of the tong of the Black Scorpion. There are many such gangs in London.

Investigating further, the Doctor learns that there may be a connection to the Chinese god of abundance, Weng Chiang. Why are young women being kidnapped of the streets of London? What is happening to them and why is a giant rat being used to guard the sewers under the streets of London? What connection is there to the Palace Theatre and can the Doctor rely on the theatre manager, Henry Gordon Jago and the local pathologist Professor Litefoot?