I have been waiting for this book for a long time, not least because I had thought it was a trilogy, rather than a quadrilogy. Here, we finally get a conclusion to the intricate plots that de Pierres has been developing and tangling over the series: Mira Fedor and her pregnancy, Trin and his semi-willing followers on Araldis, Tekton and his bizarre free-mind/logic-mind… and my favourite, Jo-Jo Rasterovich, the deep-space miner irrevocably changed by his encounter with the entity, Sole, who – it becomes increasingly clear – has something to do with everything that’s going on.

In terms of plot, there is little that is absolutely new in Transformation Space. It’s a book of climaxes, of revelations, of explanations and conclusions. That’s how it should be, and it certainly doesn’t mean that it’s boring. As with the preceding three books, de Pierres writes a relentless action story, with few breathing spaces for the characters or the reader. This is unsurprising, given that Mirror Space concluded with the revelation that a Post-Species fleet was moving into Orion space, and the suggestion that this was somehow connected to the invasion of the planet Araldis.

The use of multiple strands of narrative, used to such great effect in the previous books, is continued here; and even when the narrative swings over to Trin and his followers, forced to hide away and spend all their energy hiding and foraging, it’s not exactly relaxing, as tempers run high and eventually boil over. Other strands are more event-based. A new strand is introduced, that of Balbao, in charge of the installation commissioned to examine Sole; things go radically wrong, leading to them eventually teaming up with Lasper Farr. (Anyone familiar with the preceding books will know that such a match is bound to end badly, or at least chaotically.) Even Mira gets a fairly action-oriented story, as she gives birth and then must decide what she and the biozoon Insignia are going to do about the Post-Species fleet and Mira’s own planet. While occasionally in the other books it was sometimes disorienting to switch rapidly between characters and places, I was fairly comfortable with it by this stage. Plus, there was more convergence than ever, with various characters finally coming together or with storylines coming to a natural conclusion.

The characters are a fascinating aspect of this series for me. Half the time I can’t figure out whether I care about many, or indeed any, of them. I have never found Mira particularly engaging as a character; although sympathetic, I was frequently annoyed at what I saw as a lack of gumption. I was pleased that this book finally saw her exercising more agency, and holding her own against various other forceful personalities. This development makes sense, too, over the story; coming from a restrictive world like Araldis, a feisty female character would have been unbelievable. As she is away from that environment for longer, and is exposed to different attitudes and forced to look after herself, she responds and grows appropriately. As for the other characters: I have never felt much sympathy for Trin, the spoilt little rich kid forced to become a leader, and that didn’t change. Tekton, the arrogant tyro drawn away from studying Sole, continued to be repulsive yet oddly charming (a description I’m quite sure he’d be immensely flattered by), and I really enjoyed that he was even more active, rather than largely reactive, this time. The same cannot be said, I think, for Thales, who continued basically to be the hapless scholar; although he is involved in important events, he rarely seemed to be directly involved with them. Rather, he was more like flotsam on the tide, being pushed around and only occasionally interacting. This actually makes him quite an interesting character, I think, given how rarely such a character is male – and an educated male at that. There are other characters, of course, but it would be boring to go through all of them; they are marvellously varied, with few stereotypes and frequent surprises. I just don’t find many of them actually likeable. This makes it quite odd, I guess, that I really enjoyed this book and the entire series. It’s a tribute to the skilful writing, and the utterly intriguing plot.

The Sentients of Orion is a complex, highly textured and riveting space opera. It’s set across an entire galaxy populated by ‘humanesques’ and other, more alien beings; the action veers from intense family drama to planet-wrecking destruction. It considers genetic engineering, religion, politics, personal responsibility and the different forms love can take. It’s both character and plot-driven, and the conclusion totally astounded me. This is a series that has changed my way of thinking about space opera, and the characters that populate it.