Earth, the future. The genius Sylvest twins, child prodigies, are kidnapped by the mysterious Professor Edgeworth and taken to the planet Jaconda. But who is Edgeworth? Why does he serve the giant slug Mestor? And what is Mestor's plan?

A course change that takes the Hyperion III closer to a black hole could prove unwise when there are so many aboard ship with hidden agendas. Disappearances continue, a murderer remains at large, and one person finally crumbles under the strain of harbouring a guilty secret.

The Doctor takes Peri to Titan 3, a desolate hunk of rock in space where he hopes to find some solitude for a while. Instead he finds the lone but unconscious survivor of a recent spaceship crash in sight of a mound-shaped complex where no formalised structure should exist.

The Doctor arrives on Jaconda, once lush and green, to find it completely devastated by giant gastropods. Old legends about the planet's half-human/half-slugs weren't just myths after all. With or without help from the Doctor and his unpredictable mood swings, Lt. Lang is up for rescuing the twins, who are finally informed of the grand purpose they've been brought to Jaconda to accomplish.

The Doctor and Edgeworth deduce that the real plan of Mestor, the gastropod ruler of Jaconda, will not only destroy Jaconda but lead to the devastation of other planets. Together they hope to thwart him despite his formidable ability at slipping into people's minds and controlling them.

The Governor forces the Doctor to tell him the true value of zeiton-7 but Sil attempts to derail his plans by subjecting Peri and Areta to an enforced mutation.

The planet Karfel, in the distant future. The tyrannical Borad rules with an iron fist, and any who oppose him are cast into the Timelash - a space-time tunnel leading to the past of an alien world called Earth...

The Borad accepts no opposition and enables Maylin Tekker to expose the rebels and trap Peri with the Morlox. The Doctor tries to avert a war between Karfel and the Bandrils.

With the prosecution case concluded, at last the Doctor is able to present his evidence. It takes place in the future with a new companion and new problems.

As the Hyperion III continues its journey, more mysterious deaths occur.

With factions vying for control of the ship, the Vervoids are found to be responsible for the many disappearances. Only the Doctor sees the fundamental but missed point as to why they can't be reasoned with or why they can't be allowed to arrive on Earth.

The TARDIS materialises on a deserted beach where the Doctor and his friends are captured by primitive warriors and taken to the fabled city of Atlantis.

The Doctor and Vicki are taken before the Animus but the isoptope is left behind in the laboratory.The only hope of victory lies with Barbara and her Menoptera allies.

The former prison planet Varos, the future. The downtrodden population of miners are kept happy by real-life violence and murder broadcast live from the Punishment Dome. But then the TARDIS materialises inside the Dome...

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.

The Doctor is forced to co-operate with the Animus but Ian uses the opportunity to make an escape attempt.

Ian and Vrestin are captured by the subterranean Optera while Barbara and her Menoptera allies attempt to escape from the slave camp.

With Zaroff's plan nearing completion, the Doctor and Ben realise the only way to save the world is to destroy Atlantis.

The Doctor, Ian and Vicki are captured by the Zarbi while Barbara meets up with the butterfly-like Menoptera who are trying to reclaim the planet.

Barbara and the surviving Menoptera take refuge in the Temple of Light while the Doctor and Vicki attempt to escape by taking control of a Zarbi.

While Ara tries to save Polly from being turned into a Fish Person and Ben and Jamie try to escape from the mines, the Doctor discovers the full extent of Zaroff's plans.

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.

While the Doctor continues to play the Trilogic Game with the Toymaker, Steven and Dodo are involved in a deadly game of musical chairs.

Steven and Dodo are forced to cross the dancing floor, where the Toymaker's dolls plan to force them to dance for eternity.

The Doctor and Ramo are sentenced to be sacrificed to the goddess Amdo and must escape to put a stop to Zaroff's plan.