Benny and Jason are vacationing on the planet Phaaag Zenbrou, where the visiting Isaac Summerfield is looking after Peter while Jason and Benny try to conceive a child of their own. Following the destruction of all life on the Mimsphere, however, Benny is torn between her desire to have a child with Jason and her fear of bringing new life into a world where nothing is safe. As she ponders this, she is contacted by a Mim diplomat named Lwpha who asks her to help him rescue his children from the planet Proxima Longissima. During the war, eight million Mim evacuated from this colony world, and in the confusion and panic, a colony of Mim children -- a borogove -- was accidentally left behind. Benny advises Lwpha to appoint her the children's godmother, which gives her a legal pretext to inquire about them. Jarith Kothar, the Draconian currently in charge of the Braxiatel Collection, denies the presence of a borogove on Proxima Longissima and advises Benny against visiting the planet, claiming that the presence of surviving Mim insurgents would make it too dangerous. Nevertheless, Lwpha convinces her to investigate his claim in person, to find evidence of the borogove's existence, and to expose it to the galaxy so the Draconians will be forced to let the children go.
Benny and Lwpha travel to the Mimsphere inside an old space wreck; the planet's orbital defences classify it as junk and allow it to burn up in the atmosphere, and the survival pod hidden inside splashes down safely in the ocean and is hidden amidst the debris. Lwpha takes the form of a Draconian soldier, and he and Benny head for a research pontoon set up above the borogove's last known location. On the way, Benny inquires about Mim biology, and although Lwpha is reluctant to reveal too much to her, he does explain that the Mim, like all forms of sentient life, evolved from a collection of cells that learned to co-operate with one another. Most life in the galaxy evolved from sponges; on the Mimsphere, sponges themselves evolved the ability to shape-change as a defence against predators. Mim reproduce asexually by budding, and their young group together in a cluster where they slowly develop into individual sentient beings, trained to mimic any form of life, survive in any environment, and even reform themselves if cut into pieces.
Lwpha delivers Benny to the pontoon, claiming that she's a biologist named Frymer who was stranded on the planet when the Draconians invaded. The Draconians test Benny's blood, but accept Lwpha at face value, since it's too time-consuming to test every Draconian soldier on the planet and it's assumed that Mim civilians would be unable to mimic a Draconian convincingly. Benny is put to work with Lady-Captain-Savant Cheset, one of the few Draconian females permitted to pursue an intellectual career; she's studying Mim biology in order to figure out how a mass of undifferentiated tissue can think, and she believes that the borogove has migrated from its original location and has since been hidden. Benny is horrified to learn that Cheset has been conducting an autopsy on a dead Mim child that she claims to have found on the seabed, but Lwpha believes that it probably died accidentally when the borogove migrated. The official Draconian stance is that the Mim only mimic sentient behaviour, and that they abandoned their borogove because they don't care for their children; this is presumably to make the destruction of the Mimsphere more palatable to the rest of the galaxy. However, Cheset is interested in finding out the truth, not just supporting official policy. Benny wonders whether Cheset would make a useful ally, but before she can decide, the pontoon explodes.
Lwpha's body shields Benny from the brunt of the explosion, but he is widely scattered, and Benny is left treading water alone for hours until he pulls himself back together. When they are seen together, they are contacted by a cell of insurgents who had no idea that there were other Mim agents aboard the pontoon when they blew it up. The saboteur, Spong, smuggled explosives onto the pontoon's supports by dividing his body into nine pieces too small to trigger the Draconians' perimeter defences. He and Benny try sharing jokes, but find that their species' sense of humour doesn't translate well. Once Benny has recovered from her exposure to the elements, Lwpha takes her to see the borogove -- and, astonished by its size, she realises that there's something Lwpha hasn't been telling her. He is forced to admit that, out of the thousands of offspring in the borogove, only a few hundred will survive to adulthood. This is a natural part of Mim biology and childcare; caring for each individual bud in the earliest stages of growth would be like caring for each individual gamete in a human body, and some human embryos. The Mim care for every child that develops to term, and even though many Mim contributed offspring to this borogove, Lwpha loves each of them as if they were his own. The Draconian position that the Mim don't care for their children simply isn't true -- and the fact that this borogove was abandoned implies that the mass panic during the evacuation was somehow manufactured.
Lwpha and Spong escort Benny to the human embassy, and on the way, she tells them about her future child Keith and the sense of loss she experienced when that future seemed to disappear before her eyes. Lwpha admits that he'd probably prioritise saving other Mim's children, because he could, genetically at least, replace his own. Their boat is then spotted and blasted out of the water, and although Benny and Lwpha manage to abandon it in time, Spong is severely burned and loses most of his soft tissue. As he dies, he admits to Benny that his people have taken deliberately silly-sounding names in order to sound harmless to humans, and Benny tries to offer him comfort in return by telling him about human beliefs in the afterlife. She and Lwpha are now stranded without a boat in the middle of the ocean; Mim insurgents won't risk trying to rescue them now that they've been spotted, and Draconians won't be searching for survivors. Benny thus broadcasts a photograph of herself from her camera-phone, relying on chance to determine who finds them first; fortunately, a boat from the human embassy arrives just seconds ahead of the Draconians, and although the Draconian gunboat harasses them all the way back to the embassy, they're unwilling to risk a diplomatic incident by firing first.
Once safe in the embassy, Benny releases her photographs of the borogove to the galactic media. But the Draconians unexpectedly respond by revealing that there are several other abandoned borogoves on the planet. Records of their existence and the lives of their parents were presumably lost in the destruction of the Mimsphere, and now the public perception will be that the Draconians have a moral right to raise the borogoves, which the Mim obviously abandoned to save their own lives. The Draconians offer to send Benny back home with no repercussions, but Benny risks her life by allowing Lwpha to shed most of his mass and diffuse into her bloodstream so she can smuggle him off-world. She is shaken when her blood is tested at the spaceport, but somehow she passes the screening and is able to get back to the Collection, where Lwpha diffuses back out into her bathwater. Once he's reformed, Benny tells him that the Collection will be hosting negotiations between the Draconians and Mim on the subject of the borogoves, and Lwpha thanks her for her bravery, which may have saved thousands or even millions of Mim children.
- The Mim have a colonly world called Proxima Longissima. The Mim name for it translates as "Holiday Home".
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