The violent, volcanic world of Hephastos is home to a colony of composers, painters, authors and poets, all striving to create the greatest works of art the universe has ever seen. But in pursuit of their goal, artistic collaboration has been taken a stage too far...
When the Doctor and Romana arrive, they discover the colonists have neglected their well-being and their once beautiful habitat, which has now succumbed to decay, and they are enslaved to the Babble network which occupies their every waking moment. Every thought, however trivial or insignificant, is shared with everyone else and privacy is now a crime.
The colonists are being killed and the Doctor and Romana begin to suspect that a malevolent intelligence is at work. With time running out, the two time travellers race to discover the truth before they too are absorbed into the endless trivia of the Babblesphere...
The Doctor and Romana II - and K9, though he is not seen - land on the world of Hephastos, which has a small human colony of about ten thousand people. Immediately before they materialise, a man staggers into the street, spouting trivia about his day... then dies suddenly, smoke pouring from his ears. Visible on his head is an electronic interface chip, wired into his brain.
Accused of murder, the Doctor and Romana are taken into custody by a hostile robot. It is surprised to discover they lack interface devices, and takes the Doctor away to be fitted with one, promising Romana that she is next. While he is gone, Romana meets another prisoner, Aurelius, who explains the situation. The devices are brain links that connect every person on the colony to a central computer network, called the Babble network. At one time they were voluntary, but now they are compulsory; the central computer, the Prolocutor, controls the planet, and private thought ("clandestination") is a crime, of which Aurelius is guilty. He has found ways to hide his thoughts from the network, and must suffer for it.
The duo escape the cell, and meet a most unlikely group of rebels: a crowd of elderly women who have managed to remove the devices, and now live beneath the notice of the Prolocutor—or so they believe, at least. Together they rescue the Doctor, who has just completed testing prior to the implantation procedure. They make their way to a subterranean control room, where they find more of the Babble network's history—and the skeletons of its original controllers, sitting where they were when the Prolocutor killed them and seized control. They are just about to end the machine's reign, when Aurelius turns on them.
Speaking with the voice of the Prolocutor, he tells them that he was planted in the cell by the computer to engage and then betray the Doctor and Romana, and bring them into the Babble network's control. Although Aurelius had believed he had free thoughts, he was mistaken; his implant was only temporarily disabled, and now had been reactivated. The computer forces the Doctor and Romana to join the network, not via implant—which they will eventually have, once incorporated—but via the more primitive headsets the original operators had used.
Once connected, they find themselves inside the virtual Babblesphere, a digital world populated by the minds of everyone on the planet, endlessly spewing their thoughts to each other. The Prolocutor reveals its plan: The rebels had previously sent a distress signal, and the Empire will not ignore it. Once help is sent, they will be absorbed into the sphere, and their ships will be used to reach other worlds, until the Prolocutor controls the Empire. Unfortunately, it reveals its weakness as well: It cannot deal with the vast amounts of trivia flowing through it. What people eat, what they wear, how they feel... these things are driving it insane. To lighten the burden, it has begun to kill off the worst offenders, like the body beside the TARDIS.
This gives the Doctor a plan. While he distracts the computer, Romana rouses the masses inside the sphere and leads them to ramp up the trivia they are pouring out. Still, this is not enough to stop the computer—until the Doctor and Romana join in. With the weight of all the minutiae that a Time Lord's long life accumulates, they begin to overcome the machine.
In the midst of this, a new voice arises - that of the Eleventh Doctor. The Fourth Doctor quickly deduces that it is a future incarnation of himself (and takes a moment to insult his relative physical youth, of course). The Eleventh Doctor tells him to save a copy of the Prolocutor's program and send it to an artificial intelligence museum on a hard drive—and then he adds a burst of trivia of his own, driving the Prolocutor to self-destruction.
As the Babblesphere collapses, the Doctor and Romana free themselves, and the Doctor moves to save the program as requested. He gets it, and adds a little something extra—a copy of his own psyche, to keep the program company in its exile. After all, it's not an evil mind, just lonely. Then, twenty-four hours later, with the colony experiencing a remarkable turnaround, they return to the TARDIS and go on their way.
- The Prolocutor wants to take over the Earth Empire.
- Hephastos has several thousand colonists.
- The Eleventh Doctor's top five enemies are Ice Warriors, Ood, Mandrels, Bandrils and, at number one, Chumbleys.
- The Doctor mentions that he catered for Alfred the Great.
- Romana mentions five former Time Lord Presidents: Morbius, Slann, Pandak, Pandak II, and Pandak III.
- Five TARDIS components that are always breaking down are: the fluid links, the chameleon circuit, the dimensional stabiliser, the synchronic feedback circuit, and the gravitic anomaliser.
- After Aurelius describes the Prolocutor's influence over the residents of the colony, Romana comments that they don't treat the computer as a deity and "run around in skins". (TV: The Face of Evil)
- When listing inane trivia, Romana refers to characters she knows from nursery rhymes — Rassilon, (TV: The Deadly Assassin) Zagreus, (AUDIO: Zagreus) Salyavin, (AUDIO: Shada) the Shakri (TV: The Power of Three) and Krafayis. (TV: Vincent and the Doctor)
- The Doctor knows about Romana's sonic screwdriver. (TV: The Horns of Nimon)
- The Doctor says he's trying to repair K9. (TV: The Leisure Hive)
- The Eleventh Doctor makes a surprise appearance as the Fourth Doctor and Romana are making up "top five" lists, similar to his cameos in AUDIO: Shadow of Death and AUDIO: Vengeance of the Stones. The Doctor suggests that he is not unfamiliar with encountering future incarnations of himself. He also accurately describes the Eleventh Doctor as being very young in appearance, despite only having a voice to go by.
- Romana uses her knowledge of the flutterwing to defeat the computer. (TV: The Pirate Planet)