While Braxiatel is away on business, Benny receives a call from Dominic Troy, a handsome young man who claims to have found the lair of the planet Hera's legendary Soul-Sucker. According to legend, Avril Fenman was squire to Knight Cherry of the female Knights of Rowan, until one day she abandoned her knight to a murderous band of goblins whilst she took a crystal with the power to steal souls. She was condemned to death for her crime, but used the crystal to switch bodies with her executioner at the last moment and then began a reign of terror, moving from body to body to escape death while fighting to destroy the Knights of Rowan. The remaining Knights eventually defeated and imprisoned her, and until now it has been believed that they did so somewhere on Hera. However, Dominic works for Braxiatel's rival collector Arsine de Vallen, who has recently found proof that the Knights of Rowan, while unaware of the existence of life on other worlds, did possess spaceflight capabilities. Dominic believes that they hid Avril's body on a nearby asteroid and then destroyed all of their own spacecraft so that nobody would ever be able to free her... and he believes that the asteroid in question is the current home of the Braxiatel Collection.
Benny finds it unlikely that such a cavern could have been overlooked in the initial surveys of the asteroid, but she does arrange a visitor's pass for Dominic. Even the fearsome Ms Jones is quite taken by the handsome Dominic, and Benny allows herself to get a little too drunk while dining with him in the Mansionhouse that night. Their dinner is interrupted when Adrian Wall, the Killoran construction engineer, announces that his team has just broken into a large cavern which didn't appear on any of the surveys. Benny tries to contact Braxiatel, but she can't get through to him, and thus decides to check out the cavern herself. As Dominic had suspected, this is in fact the tomb of the Soul-Sucker, but Benny is already starting to have doubts about Dominic's true intentions; he seems to be taking too much care over his physical appearance, and when Benny refuses to let him touch the body he threatens her. Although he claims that he was joking, she realises that he has some other agenda, and takes him back to the Mansionhouse, promising to excavate the tomb properly the next morning... but in fact ordering her porter Joseph to keep an eye on Dominic and warn her should he try to leave his guest quarters.
Unfortunately, Dominic short-circuits Joseph before he can sound an alarm, and Benny finds out the hard way that he'd already drugged her wine during dinner. When she next awakens, she's in the crystal, and Avril's mind is in Benny's body. Dominic just wants the crystal, and he's used Benny to prevent Avril from overpowering his mind and taking his body... but Avril will not risk the possibility of Benny's taking her body back, and before Dominic can stop her she smashes the crystal to pieces. Benny is now discorporate, and it takes all of her willpower to hold onto her existence and follow Dominic and Avril back to Hera, where Avril has promised to take Dominic to the original crystal cavern. She manages to hold on long enough to see Dominic call an ally, and to watch as a beautiful young woman follows Dominic and Avril out of the Hera spaceport -- but she is unable to resist the pull of the crystal cave any longer, and finds herself trapped in the crystals, unable to escape, and surrounded by the discorporate souls of Avril's past victims.
Dominic and Avril arrive, but Dominic is overwhelmed by the power of the crystals and loses his mind to them. This is just as Avril expected; she would never have brought him here otherwise. Before Avril can shoot Dominic's now empty body, the young woman rushes in and tries to shoot Avril. In the confusion, Benny senses Dominic's empty body nearby and enters it, just as the other two women's shots go wild and the cavern, damaged by the gunfire, begins to collapse. Avril flees, and the girl, believing that Benny is Dominic, helps her to escape. Benny picks up a crystal as they flee, but doesn't tell the girl; instead, she claims that they have to follow the escaping Avril to get back the crystal. They are too far behind her, however; by the time they reach the spaceport, Avril has already boarded the shuttle back to the Braxiatel Collection. Since Avril looks like Benny and Benny looks like Dominic, and Dominic's pass was good for only one visit, the guard refuses to let the real Benny past. Guards from de Vallen's estate then arrive to demand an explanation for Dominic's apparent attempt to flee, and confiscate the crystal from Benny. Benny is forced to watch helplessly as the shuttle launches, taking Avril back to the Braxiatel Collection in Benny's body...
Benny's behaviour has given Dominic's girlfriend the impression that he was trying to betray her. Unfortunately, she forgives him, and to Benny's horror she finds her new male body instinctively responding. Once back on de Vallen's estate, she bluffs their guard into giving her a new security code for their rooms, where she evades the girl's attentions and steals her knickers, which Benny finds far more comfortable than Dominic's own underclothing. She then settles into the bath with the book which Dominic had used to research the legend of the Soul-Sucker, and at last learns that Dominic's girlfriend is named Poppaea Prince. She also finds some rather disturbing annotations, which seem to imply that "Dominic Troy" is in fact Nico Lyence, a war criminal who was believed killed after he used his near-mythical good looks to gain power in the Fifth Axis. Lyence never allowed his photograph to be taken, but there are those amongst the Fifth Axis who still want him dead -- and somehow Benny must get the crystal back from de Vallen, get back to the Collection and switch bodies with Avril again, while stuck in this war criminal's body.
Poppy still believes Benny to be Dominic, and despite herself, Benny feels guilty for possibly traumatising Poppy with the belief that Dominic no longer loves her. Worse, Benny's new male body tends to react instinctively to Poppy's advances, and trying to hold things in place with sticking plaster proves utterly disastrous (and very painful). And even worse, while drifting off to sleep Benny hears Dominic's voice raging in the back of her mind, and realises that his soul is trapped in the crystal which is now in de Vallen's possession; as soon as she lets down her guard, he'll try to take his body back. She resists him for as long as she can, but she finally does fall asleep; however, by that time Dominic has another agenda. While resting in the crystal, he has heard de Vallen murmuring to himself in triumph; tomorrow, de Vallen will announce to the staff that he has named Dominic as his heir, and he will then poison himself and use the crystal to move his soul into Dominic's body. Dominic is enraged, but now he has had more experience in soul-switching than de Vallen, and he therefore decides to wait for de Vallen to stun Benny, and use the opportunity to take back his body and keep de Vallen out.
Back on the Braxiatel Collection, Ms Jones has been appalled by Benny's uncouth behaviour since her apparent return; but that's going to be the least of the real Benny's worries. Unfamiliar with such modern conveniences as baths, beds and fireplaces, Avril has built a fire in Benny's room, pulled all of the pillows and duvets from the bed and sprawled out naked atop them; and this is how Adrian Wall finds her when he arrives to complain about the signs which Benny left to prevent his men from disturbing the tomb. When Braxiatel finally returns, he finds Ms Jones in quite a state, and Adrian Wall head-over-heels in love...
The next day, de Vallen announces to his personal staff that he has willed his entire estate to Dominic Troy, and invites "Dominic" to his suite to tell him the good news. As soon as he and Benny are alone, he stuns her, drinks a vial of poison and prepares to use the crystal -- but thanks to Benny's earlier behaviour, Poppy believes that Dominic is trying to cut her out of the deal, and she thus stuns de Vallen's guard and bursts in to confront Dominic. Instead, she finds "Dominic" unconscious, and helps Benny to escape. The guard Bill stumbles in, recovering from the stun blast, and the dying de Vallen tells him to look into the crystal -- but Dominic acts before de Vallen, and gets into Bill's body first. When he studies the vial and realises what de Vallen had intended for him, he leaves the old man to die in his own body. He then pursues Poppy and Benny with the crystal, intending to take his own body back, but he catches sight of his new body in a mirror and is so horrified that the women escape before he can pull himself together.
As de Vallen's chauffeur takes Benny and Poppy to the spaceport, he happens to mention the news of Dominic's inheritance. Poppy is delighted at first, but then realises that there is now no need for them to leave the planet. She thus concludes that "Dominic" must be pursuing "Benny" because he's fallen in love with her. Furious, she stuns Benny and orders the chauffeur to turn back to the mansion, refusing to let Dominic cut her out. The real Dominic thus catches up with them and manages to explain the truth to Poppy at last, but Benny recovers from the stun blast and bluffs them into pulling back by holding a bottle of stain remover over her hand and claiming that it contains acid; if Dominic tries to stop her, she'll damage his perfect skin. She thus reaches the spaceport, where she uses the time before the next Braxiatel shuttle leaves to take photographs of Dominic's body -- or rather, Nico Lycene's -- and mail them to a Pakhar investigative journalist with instructions to reveal the truth about Dominic should she fail to receive word from Benny within a certain amount of time.
Dominic and Poppy arrive, accompanied by de Vallen's guards Chevy and Rix, who accuse Benny of murdering de Vallen in order to gain his inheritance early. Dominic has confirmed this while pretending to be the guard Bill, but he realises too late that this means he can't move back into his old body without standing accused of murder. Benny thus strikes a deal with him and Poppy; if they return to the Braxiatel Collection and help her to get her old body back, she will allow them to return quietly to claim their inheritance. Dominic reluctantly tells Chevy and Rix that he was mistaken, and, although puzzled, Chevy and Rix release them all and return to the mansion to investigate de Vallen's death. Benny, Poppy and Dominic then try to catch the Braxiatel shuttle, only to find that it's been cancelled due to lack of passengers. When they insist upon leaving, the steward -- already put upon by the uncouth Avril during the last flight -- gives up, quits his job and leaves them to try piloting the shuttle themselves. They steal the shuttle and depart, but are hotly pursued by police from Hera -- and by Chevy and Rix, who have found Bill's fingerprints on the vial which Dominic examined, and have concluded that Dominic, Poppy and Bill are all in on the plot together.
Fearing that Dominic and Poppy may try to take back Dominic's body before she's ready, Benny reveals that she took photographs of herself in the spaceport, and forces them to lock up the crystal in a passenger safe which only Benny can open. Unfortunately, as they draw nearer to Braxiatel jurisdictional space, the pursuing ships open fire, and Dominic panics at the thought that his perfect body might be bruised or cut. He and Poppy thus smother Benny unconscious and stuff her in a locker, padded and protected with pillows and linens. Unfortunately, Dominic isn't as skilled a pilot as Benny, especially while trying to get used to the reflexes of his new body, and he thus crashes the shuttle on the Braxiatel Collection. With Adrian Wall's help, they escape moments before the shuttle goes up... taking the crystal with it.
When the narcissistic Dominic realises that he may be stuck in Bill's body forever, he nearly commits suicide, but Benny manages to convince him that Avril must have a crystal of her own -- or so she hopes. Since they are all apparently trespassing, they are locked up without the opportunity to speak to Braxiatel, but Benny knows enough about the guards' private lives to convince them to let her speak to Broderick Naismith, Irving's right-hand man, whom Benny has never in fact met personally. While waiting, however, Benny sees Avril skinny-dipping in the fish pond, in her body, with Adrian Wall, and realises that time is of the essence. Dominic and Poppy thus create a distraction while Benny breaks out and tries to get word to Braxiatel. Recalling Ms Jones' earlier reaction to Dominic, she uses his body to flirt with her and get a security pass, claiming she wants to tell "Benny" that "Dominic" survived the collapse of the cavern. Before returning to her rooms, she writes a note to Braxiatel, and then storms off to confront Avril... but Avril refuses to return Benny's body to her. She's rediscovering the joy of sensory input after spending a thousand years in the crystal, and she has no intention of giving it up now.
To Benny's horror, Avril tries to seduce her, and Dominic's body begins to respond... and then Adrian arrives to propose to the woman he believes is Benny, sees what's going on, and flies into a jealous rage. Fortunately for the real Benny, Braxiatel gets her note and arrives just in time to save her. Braxiatel sends Wall to collect Poppy and Dominic, who arrive greatly impressed by their audience with Naismith. In the meantime, Braxiatel questions Avril and Benny about Benny's personal life to find out who's who. Avril has read Benny's diaries -- and, to Benny's rage, she's then burned them in her fire -- but she hasn't quite grasped the point of the yellow sticky notes which Benny uses to overwrite real events with her preferred version of things, and she thus gets all of the subtle details wrong. Once Poppy and Dominic arrive and the story is sorted out, the search for Avril's crystal begins, but it is nowhere to be found... until Wolsey walks in with a dead fish which he pawed out of Braxiatel's pond, the one in which Avril went swimming earlier. All of the fish are floating on the surface, their minds drawn out of their bodies by the crystal which Avril planted in the pond.
Now it's just a question of switching bodies around, but Benny has a moral dilemma; what are they to do about Bill, the unfortunate guard whose body Dominic now occupies? Benny offers to enter the crystal to see if Bill's mind is still there, but when she leaves Dominic's body, Avril switches into it and tries to destroy the crystal. Braxiatel stops her just in time, and Benny returns to her own body. Bill's soul no longer exists; he was unable to hold onto his existence, and dissipated just as Benny nearly did earlier. But in the confusion, Dominic and Poppy escape and force Braxiatel to hand over the crystal; they have big plans for it. Avril doesn't care which body she possesses, just as long as she has a body, and Braxiatel thus hands over the crystal to Dominic -- in Bill's body. When Dominic and Avril switch bodies, Dominic realises too late that Avril is now holding the crystal, and before anybody can stop her she smashes it to pieces so nobody can force her to go back. A fragment rebounds from the floor and hits Dominic in the face; it's just a shard, but according to Braxiatel, it's now embedded deeply enough to do worse damage and leave a permanent scar if they try to remove it. Dominic, realising that he is no longer perfect and never will be again, smashes his hand into Benny's mirror in a fit of anguish, scarring himself for life.
Dominic and Poppy are taken away to be charged with their war crimes, but to Benny's disgust, Braxiatel decides to allow Avril to live in the Collection, in her former tomb. Avril claims that she fell victim to the crystals by accident while fighting to save Cherry from the goblins which once lived in the cave. She fought off the pull of the crystals too late, and tried to take Cherry's body back to civilisation to tell the Knights about her death; but she couldn't make it, and thus used the crystal to send her mind out into the countryside and summon help. When she was found, however, she was accused of witchcraft and of betraying her knight, and was sentenced to death without a hearing. Realising that Cherry's family would never learn the truth of her death, Avril realised that the Knights were corrupt and fallible, and from that day forth she dedicated her life to destroying their power. But Benny is too humiliated and angered by her experiences to trust Avril, and there are still issues left unresolved. There's the mortally humiliated Adrian Wall to deal with, for one... and were all the crystals really destroyed when the cave collapsed on Hera?
Some time later, a young man selling his body in the bars on Syal is contacted by an old man who warns him not to answer a certain advertisement in the papers. It may seem at first to be the opportunity of a lifetime, but in fact it's a lure for an industry set up by a beautiful young woman to move dying old millionaires' souls into younger bodies. It appears that Poppy, at least, has found another crystal and a lucrative use for it...