While sleeping off a headache in her quarters on the Braxiatel Collection, Benny hears a young woman’s voice in her head, screaming in despair as her masters cut out her friend’s tongue. Horrified by what she’s hearing, Benny tries to communicate with the woman, who is equally startled to hear a voice in her head. Benny learns that the young woman has no name, only a number -- 26 -- and, moved by 26’s terror and despair, Benny vows to find and help her. Jason is reading bedtime stories to Peter when he sees Benny walk out into the snow in her nightie; he follows her out and tries to wake her, but she knocks him aside and boards Braxiatel’s private shuttle. Jason follows her on board, but Benny takes off before he can strap himself in.
Meanwhile, the sleeping Benny is still communicating with 26. She learns that 26’s people are humanoid, with two arms, two legs and two eyes -- and for some reason, their masters hate them for this. Most of the slaves are mute, and those who develop speech are punished by their masters, forced to give up either the power of speech or one of their other senses, such as sight or hearing. Most who have developed speech choose to lose their tongues, but one of 26’s other friends, 44, chose to have his eyes put out instead. 44 has since escaped, and Benny vows to help the terrified 26 escape from her cruel masters as well.
The shuttle lands on a distant planet, and when Benny emerges, she is confronted by two of the slaves’ masters, one-eyed green aliens with untidy mops of hair. The aliens, Zarf and Rezram, are horrified to hear Benny speaking aloud in her sleep, and they seize her and prepare to cut out her tongue. However, she is shocked awake when they grab her, and when Rezram pulls out a knife, Benny thinks quickly and pretends to be deaf. The suspicious aliens decide to take her to their leader, Hult, for questioning. As Rezram drags Benny away, 26 speaks inside Benny’s head again -- to Benny’s relief, as she was starting to think that the voice in her head had been a dream. 26 learns what has happened and warns Benny that Hult will test her to find out if she is lying; if he concludes that she is trying to trick him, she will be severely punished.
Benny suffers another twinge of headache as Rezram drags her into the aliens’ compound, a tall, white building in the middle of the scrubland; there, Hult addresses Benny and threatens her with vile punishments if she does not reveal her identity. Benny loudly protests her treatment, claiming that she can see Hult’s lips moving but can’t hear a word that he’s saying. Rezram fears that Benny is the first of a new breed of slaves with speech, sight, and hearing, but Hult points out that she could merely be a freak mutation. As they speak, 26 warns Benny that a master is moving into position outside; he will create a loud and unexpected noise, and if she reacts to it, the masters will know that she’s lying. However, 26 telepathically alerts Benny before the alien hammers against the wall, and Benny is thus prepared and does not react to the noise. Satisfied that she is deaf after all, Hult concludes that her speech is merely a random mutation; however, Rezram still fears that the slaves will develop more senses than their masters and will then rise up against them.
Back in the shuttle, Jason recovers consciousness, but he has been badly injured by the turbulence of the shuttle’s launch. Unable to walk, he drags himself into the cockpit only to find that Benny has gone without taking a communicator. He orders the computer to scan the area for signs of humanoid life, and it reports that there are ten humanoids immediately outside. Before he can react, they enter the shuttle and find him...
Rezram puts Benny to work peeling potatoes in the kitchens, and is infuriated when she begins to sing a happy potato-peeling song, apparently unable to hear his demands that she stop. The furious Rezram storms off, confident that the new slave will eventually learn the consequences of disobedience. Once he’s gone, Benny finally meets 26 in person, but as they hug, Benny suffers another twinge of headache. She is disturbed to realise that the mute slaves are unable to sing; at least slaves on Earth had music to get them through the day and give them hope. 26 then notices the necklace that Benny is wearing, and when she reveals that she’s wearing a similar necklace, Benny finally works out what’s going on. Benny’s necklace is an ancient artefact from the Halavan civilisation of Petreus III; according to legend, the planet was ravaged by natural disasters, and the best and the brightest of the Halavans left their world to search for a new home but were never seen again. The planet has since renewed itself and is an unspoiled paradise ripe for exploitation -- and although the Galactic Trust is trying to preserve it, several groups are now staking claim to the planet by claiming to be the descendants of the lost Halavans. The Trust thus authorised archaeological digs on Petreus III, and Braxiatel hired Benny out to authenticate the relics from the digs. While examining the artefacts, she donned an old necklace for fun, but then had to retire to bed with a sudden stabbing headache...
Presumably, the identical Halavan necklaces are allowing Benny and 26 to communicate -- and since nobody has set foot on Petreus III since the Halavan ship departed, 26’s necklace can only have come from that ship, which implies that she and her people are the true Halavan descendants. The Halavans were said to be telepathic, but since 26 knows of no other telepathic slaves, Benny theorises that the ability is latent and that the necklaces are necessary to boost it. If they can find more necklaces, perhaps they can give all of 26’s people the gift of telepathic speech. 26 tells Benny that the necklace was a gift from her friend, 44, but before Benny can hatch a plan to find 44, she collapses with a splitting migraine. Rezram returns, finds that Benny has collapsed, and orders her back to work -- and in her agony, Benny unthinkingly lashes out at him, revealing that she can hear him after all. Furious, Rezram drags her off to make an example of her before the other slaves.
Elsewhere, the helpless Jason is removed from the shuttle by more mute slaves and carried through the wilderness to a set of caves, where 44 is waiting to question him. Jason is appalled to see that, while his captors have no tongues, 44 has no eyes. When 44’s masters gave him the choice, he chose to retain the power of speech so that he could teach his fellow slaves to talk; he subsequently escaped, and has been joined by fellow escapees. He hopes that one day there will be enough slaves with a full complement of senses to rise up against their masters, but has accepted that this will take years. Jason can’t afford to wait that long and thus suggests an alternative plan. 44 is reluctant to leave the darkness of his caves, where he is the equal of anyone with sight, but he agrees to accompany Jason back to the shuttle, where Jason sets in motion a plan to free more of 44’s people -- and rescue Benny.
The aliens have brought Benny out into the open and summoned their slaves to witness their punishment. For some reason, Benny finds herself thinking of the aliens as Monoids -- an apt name, but one which seems to have popped into her head from nowhere. Hult addresses the slaves, telling them that Benny will be punished for her disobedience by having her ears, eyes and tongue removed. As Benny protests and the Monoids restrain her, a voice comes from the crowd, ordering the Monoids to stop -- and more voices spring up from more and more slaves who claim to have developed the power of speech. The shaken Monoids fail to notice that the slaves are all speaking with the same voice, which 26 identifies as the voice of 44. Jason then shouts from the crowd, ordering the Monoids to release Benny; frightened, they do so, and Benny rushes into the crowd, only to find that the slaves are actually wearing communicators. Jason and 44 are still on the shuttle.
44 addresses the Monoids through several different communicators, making it appear as though the slaves have developed the power of speech; since they also have the power of hearing and sight through two eyes rather than one, this makes them superior to the Monoids. Hult refuses to accept their superiority, but reluctantly agrees to treat them as equals; however, he refuses to release those who still cannot speak. Benny tries to win their freedom as well by claiming that the free humans have the right to take slaves now, but this pushes Hult too far, and he descends from his throne to confront her. Once down in the crowd, it doesn’t take him long to work out that the voices are coming out of the communicators and not the slaves. The trick exposed, Benny tells the slaves to flee, and she and 26 join the mass breakout. Unsure in which direction to run, Benny tells 26 to take charge -- which, after a life of slavery, 26 finds very gratifying indeed.
Jason sends another of 44’s fellow fugitives, 89, to lead Benny back to the shuttle; 26 identifies him by number, but when Benny greets him on 26’s behalf, the suspicious 44 demands to know how Benny knows 89 when they have never before met. Benny promises to explain once they arrive at the shuttle, and is appalled to learn that she apparently injured Jason terribly when she took off back on the Collection. 26 is puzzled by her relationship with Jason, and Benny explains that Jason is supposed to be her life partner -- and although things don’t always work out well between them, she misses him when he’s not around. Benny and 26 are then reunited with Jason and 44, and Benny explains the strange properties of the necklaces to 44. Sadly, though 44 sacrificed his sight in order to keep the power of speech, it seems that his people don’t need speech to communicate after all.
44 leads the others back to the caves, explaining that he once sheltered here from a rainstorm when he got lost on a work detail. He experienced a strange feeling in their depths, and thus fled in fear; when his eyes were taken, he returned here in order to hide, but he has never ventured as deep into the caves as he did the first time. He does so now, and this time he and 26 both begin to feel strange -- and Benny suffers another piercing headache. By now, she’s worked out that she’s suffering these headaches because her human brain is only partly compatible with the Halavan necklace; nevertheless, she keeps the necklace on in order to communicate with 26 and help locate the ship. Eventually, 44 finds a hatchway hidden behind the rocks, and Benny sends 26 and 44 through first, telling them that it’s their right to take the first steps into their ancestors’ ship.
The interior of the ship is astonishingly beautiful -- until Benny finds a cupboard containing a strange machine and a heap of old bones. 26 realises that the machines on the ship boost the Halavans’ latent psi powers; they are already exerting their influence through her necklace, and she finds that she can remember what happened here. The crash was no accident, but the result of fighting between the Halavans, who disagreed on which direction to take the ship and were unable to co-operate long enough to repair the damage caused by their battle. The survivors fought until only one faction remained -- or so they thought. But when they went out to conquer this planet and make the natives their slaves, they left behind one surviving enemy, a young woman who destroyed the telepathic boosters and caused the ground to swallow up the ship. Unable to communicate with one another, the now-helpless Halavans were easily conquered by the Monoids, and they have been slaves ever since. But now that 26 is in contact with the ship, she can reactivate it and restore her people’s telepathic powers.
Jason and 44, unable to hear 26’s telepathic exposition, watch in confusion as she uses her necklace to repair the damage to the ship. Benny collapses in agony, and Jason forcibly removes her necklace, cutting her out of the gestalt that is forming between the former slaves. However, she’s sensed enough to realise that things are not going the way she wanted. 44 and 26 are now able to communicate, and they transport the ship to the Monoid compound; Benny now realises that the Monoids were named by the original Halavans, and that the necklace planted that name in their mind. The Halavans use their new abilities to force the Monoids aboard their ship, and 44 addresses Hult, revealing that the Monoids’ greatest fear has now come true; their slaves have more power than they do. The time has come for the Monoids to pay for their crimes -- by losing their own ability to speak. Benny protests, but to no avail, as the Halavans turn the power of the gestalt upon the Monoids and seal their mouths up forever. From now on, the Monoids will have no individual names or identities -- and the cruel Rezram will be known as 44.
Sickened, Benny reveals to Jason that she glimpsed the race memories of the Halavans while inside the gestalt; the Halavans destroyed their own planet by misusing their mental powers, and the rich and elite fled from their dying world, leaving the rest of their people to die. They then fought amongst themselves, causing the ship to crash here. Benny dons her necklace once again and tries to reason with 26, but the former slave is taking a fierce glee in her new powers -- and she reveals that her people are using their powers to destroy this planet before they return home to Petreus III. Benny begs 26 to at least take the Monoids to safety on another world rather than abandoning them here to die, but 26 refuses to let Benny address her by a number any longer; she is free, and she will choose a real name for herself. 26 rips the necklace from Benny’s throat with a gesture, and with another gesture, 44 heals Jason’s injuries and flings both him and Benny back to their shuttle. As the planet breaks up around them, Benny and Jason have little choice but to depart. They detect no life signs from the planet, which means either that the Halavans took the Monoids with them or that they killed them all before leaving. Though dissatisfied with the outcome, Benny has little chance but to return to the Collection and hope that the Halavans will settle down and become less aggressive once they return to Petreus III.