While passing the apparently unremarkable planet Hogsuum, the TARDIS detects a Fortean flicker, a temporal anomaly which displaces events and objects from their proper positions in space and time. The Doctor looks up Hogsuum in the TARDIS data banks and finds a reference to Gustav Urnst, a sensationalist author of the 25th century who vanished mysteriously after claiming to have found the legendary planet Sakkrat. It is said throughout the civilised galaxy that the people of Sakkrat reached the pinnacle of technological achievement, the Highest Science, and then destroyed themselves with it. Benny is skeptical until the Doctor suggests that the Fortean flicker could be a side-effect of this Highest Science. By its very nature, a Fortean flicker causes strange juxtapositions and apparent coincidences -- and it would certainly be a coincidence if Urnst spent his life writing about lost civilisations and ancient secrets, and then actually found one…

A Chelonian assault force fighting human parasites on the planet Vaagon is suddenly transported to Hogsuum by the Fortean flicker. The traumatic journey causes General Fakrid to give premature birth to stillborn eggs, and the infuriated general orders his troops to destroy the enemy which has brought them here. When his troops detect an energy surge in a nearby valley, Fakrid sends them into battle although the nature of the energy can’t be identified -- and the patrol is wiped out while reporting that they have encountered “eight twelves”. Fakrid and his men try to retaliate, but are driven away by smart weaponry against which they are unable to defend themselves. Meanwhile, the TARDIS materialises nearby, and the Doctor and Benny emerge and meet a drugged-out youth named Rodomonte who seems to recognise them, or at least their description. The Chelonians then arrive to investigate the energy surge caused by the TARDIS’ materialisation, and the Doctor sends Benny and Rodomonte to safety while he stays to protect his TARDIS… which may no longer be fully capable of protecting itself.

Meanwhile, another spaceship arrives in orbit, having been guided to this planet by an organic intelligence known only as the Cell. The psychopathic criminal Sheldukher, seeking to relieve his boredom, stole the Cell from the laboratories of Checkley’s World over a century ago, and placed himself and his reluctant associates into suspended animation while the Cell searched the galaxy for Sakkrat. Over the past century, the Cell has attempted to alter its physical appearance to become more efficient, but it has made several grave errors and now lives in eternal agony, wishing for death. Sheldukher, however, refuses to release it until it has led him to the Highest Science, and at last it has found a world which perfectly matches the legendary descriptions of Sakkrat. Sheldukher’s psychotic bodyguard Postine doesn’t care what Sheldukher does as long as she gets to kill people, but his other associates, master thieves Rosheen and Klift, want only to rid themselves of him and return to their ordinary lives. However, they have no choice but to assist him; Sheldukher has implanted chemical dispensers in their bodies, and he demonstrates his power over them by causing Klift to age forty years in a second. Meanwhile, the Cell scans the planet below for some sign of intelligence, and finds a powerful mind unlike any it has ever encountered before. In its eagerness to make contact it overloads the Doctor’s brain, knocking him out and allowing the Chelonians to capture him.

While following Rodomonte, Benny stumbles into a swamp inhabited by a creature which uses hallucinogenic pheromones to disable its prey. Rodomonte returns to his friends Molassi and Sendei, who, like him, were transported here from the Ragasteen Music Festival of 2112, and tells them that he’s met the pretty lady from the song. Sendei sets off to look for her, taking the psychotic Molassi’s favourite discoid to prevent him from driving off without them. Sendei has encountered the swamp predator before, and he saves Benny’s life and takes her back to the speeder. Still dazed, Benny accepts a drink from a dispenser which the boys found soon after they were transported here -- but they’re unaware that the drink is bubbleshake, a dangerous narcotic which causes immediate addiction, short-term memory loss, irritability, paranoia, and eventual death. Molassi has been drinking it for some time, and now believes that the lyrics from the classic album “Event Shift” by Zagrat are foretelling his ascension to the throne of the Wizard King. Benny realises that the similarities between the album and current events are just a coincidence, but she’s already beginning to have trouble concentrating and can’t recall why coincidences on this planet are significant… or why she should be so upset about Molassi driving off without waiting for the Doctor.

The Chelonians return to the valley of the eight twelves, where the Doctor recovers just in time to pilot the battle tank away from their enemies’ sentient energy weapons. Fakrid reluctantly decides to let the Doctor live, but only if he finds a way to destroy their enemies. The Doctor rigs up a ramshackle device from spare parts, and claims that it will only work if he is allowed to use it against the eight twelves in person. Once out of sight, he disposes of the device and goes on to make peaceful contact with a group of stranded commuters from late 20th-century Earth, who were transported here by the flicker while commuting to London on the 8:12 from Aldgate. They were only defending themselves against the Chelonians, using weapons which had been brought to this planet by the Fortean flicker. The Doctor disables the dangerous weapons and promises to help the humans return home, but discovers too late that his entire conversation has been monitored by the suspicious Chelonians. As the furious Fakrid prepares to wipe them all out, Sheldukher lands in search of the mind which the Cell had detected earlier, and transmits a signal which jams the Chelonians’ cybernetic implants, paralysing them.

The youths’ speeder runs out of power upon reaching the outskirts of a ruined city, and Molassi continues on foot, convinced that he will be crowned with ice at the Temple of the Event Shift. He demands that Sendei give him more bubbleshake, but the dispenser has run dry and Sendei is unable to do so. Molassi thus attacks him, and Sendei, whose own judgement has been impaired by his bubbleshake addiction, destroys Molassi’s prize discoid in a fit of rage. Molassi stabs Sendei to death and continues on to the Temple, where he is confronted by ghosts who probe his mind but are unable to find what they are looking for. Rejecting him as unsuitable, the ghosts show Molassi a vision of an ancient talk show during which Zagrat’s former lead singer admits that he made up the lyrics to “Event Shift” while on a drug trip, and that they don’t really mean anything. The devastated Molassi kills himself, and when Rodomonte stumbles across him, seeking revenge for Sendei’s murder, he too is probed, discarded, and shown visions which drive him to suicide. When Benny enters the Temple, however, the ghosts find what they’re looking for in her mind and allow her to live -- but she is falling victim to the effects of bubbleshake addiction and withdrawal, and she passes out in the ruins of the city.

Sheldukher forces the Doctor to give himself up by threatening to kill one of the commuters’ babies. The Doctor reluctantly reveals what he knows about Sakkrat from Urnst’s book, which was published after Sheldukher went into cryo-sleep. Sheldukher sets off in search of the ruined city described by Urnst, and almost as an afterthought, he kills four Chelonians at random to discourge pursuit. But he has underestimated General Fakrid. The humiliations he has been forced to endure at the hands of mere humans, and the interruption of his breeding cycle, have driven Fakrid into a berzerker rage, and he now intends to wipe out all of the humans on this world, starting with Sheldukher.

The Cell locates the ruined city and lands the ship, but then accesses the ship’s reactors and tries to blow it up, ending its own miserable life and taking Sheldukher with it. The Doctor is able to short-circuit the airlock and escape along with the others before the ship explodes. In the ruins of the city he is reunited with Benny, and temporarily restores her mind to working order by hypnotising her. She will still require medical treatment when this is all over -- but when she realises that the Doctor is accompanied by the infamous Sheldukher, she isn’t sure she’ll survive long enough to get it. The Chelonians arrive in pursuit, and while Postine holds them off, the others enter the Temple. There, the aged Klift’s heart gives out in terror when he is confronted by the ghosts. The Doctor seems to recognise the ghosts, but he doesn’t explain himself and instead sends Benny and Rosheen to safety while he and Sheldukher continue onwards with the Cell.

Postine manages to inflict a fatal wound on Fakrid before he kills her, and Fakrid passes on command to First Pilot Jinkwa, revealing in his dying moments that Jinkwa is his son. Benny and Rosheen emerge from the city to find themselves surrounded by angry Chelonians, but when Rosheen is killed, Benny is transported back to safety by the ghosts, who are unwilling to lose another responsive mind. Jinkwa orders three Chelonians to activate their self-destruct implants and level the city, but chooses three who have spoken out against him in public. Realising that Jinkwa is becoming corrupted by power, Trooper Ozaran tries to use his implant to kill Jinkwa, but Jinkwa, realising what is happening, orders two tanks to move between Ozaran and himself, thus sheltering himself from the blast. He then kills his own tank’s Environments Officer to prevent him from revealing that Jinkwa deliberately sacrificed other Chelonians to save himself, and orders the rest of his patrol to return with him to the valley of the eight twelves. He is unaware that the ghosts have transported the remaining two kamikaze Chelonians beyond the city, leaving it untouched by their destruction.

The Doctor, Sheldukher, Benny and the Cell pass through a slow-time conversion chamber, where they are slowed down to match the flow of Time beneath the city. Anything protected by such a slow-time field, which was just a theory when Sheldukher entered cryo-sleep, may have remained unchanged for millions of years. The Cell discovers that its mental frequency matches the frequency of the conversion chamber’s lock -- another apparent coincidence -- and when the explorers pass through they are attacked by the Monumental Guardian, the fierce robot defender of the tombs. But the Guardian merely menaces them and then retreats, and the Doctor concludes that it’s just there to frighten people. Which would support his own theory about what’s really going on. Sheldukher ignores the Doctor’s warning and continues on, only to be captured and imprisoned in a force field by two blank genetic Constructs who demand the return of Project FXX Q84… the Cell. As the Doctor suspected when he first saw the Ethers, spirits of the dead enslaved with technology first developed on Checkley’s World, this entire planet was designed as a trap for Sheldukher.

After Sheldukher stole the Cell and set off in search of Sakkrat, the consortium which owned Checkley’s World terraformed the planet Hogsuum into the image of Sakkrat to lure him in and capture him while his guard was down. The slow-time unit was set up to keep the Constructs fresh while they waited for him to arrive, but it has malfunctioned, causing the Fortean flicker. And it is the flicker which seeded the meaningless legends of Sakkrat across the galaxy in the first place. The Doctor locates the slow-time unit and removes its faulty kronos element, putting the flicker to rights, and Benny then destroys the Cell, granting it the death it has wanted all along. Having failed to recover the Cell, the Constructs melt away, and Sheldukher, realising that his great quest was all for nothing, kills himself rather than let himself be captured. As a last act of revenge, he triggers a bomb which will level the city, but the Doctor discovers that the underground complex is in fact a spaceship meant to take the Constructs back to Checkley’s World once their task was complete. He thus locates the ship’s emergency transmat, and sends himself and Benny back to the valley of the eight twelves moments before the city is destroyed.

The Chelonians have just captured the commuters and are preparing to kill them all horribly with zarathion gas. When the Doctor’s attempt to rescue them fails, he is forced to use the kronos element to freeze them all, Chelonians and humans alike, in a bubble of slow time. It isn’t the perfect solution, but he’s too tired to think of a better one and decides to leave them as they are until he can work out a way to free them. He and Benny return to the TARDIS, where the Doctor nurses Benny back to health and takes her to 1935 for a relaxing night out at the theatre. He refuses to discuss the odd malfunctions plaguing the TARDIS, however, and they depart from 1935 without ever realising that Gustav Urnst, displaced from his own time by a Fortean flicker, had been in the audience with them.