This was an amazingly well developed sci-fi romance. I loved the thought that went into the different species, and cultures that make up this book. They were so well drawn, and so interesting that they really made this book work for me. There was no one perfect group, or people and they each had their own weakness and strengths, and their societies felt just as real as their biology. In the beginning I thought the romance between Lefi and Afton might have been moving a bit fast, but then I remembered that the bond between them has been forming over a year's time, and that their first meeting in this book was not actually their first meeting. I like how well they support each other, and how Lefi helps Afton to accept, and embrace his true nature. It’s not about Lefi making that realization for Afton, but giving Afton the understanding, and space to come to grips with who he is, and how his family affected his identity. I also like how Afton accepts Lefi, and helps him recover and deal with the pain of his loss. There is no magically healing sex, but Afton is able to listen to Lefi, and to give him the space and support he needs to grieve. The secondary characters are well drawn, and feel just as diverse and nuanced as the main characters, and added much to the story. The notion of gender is explored in this story, and was very interesting. It added so much to the story. What makes a person male or female, and what meaning gender has apart from the physical. At times Afton’s, and even Lefi’s, notion of feminine identity is a bit outdated, and stereotypical. I understand it coming from Afton, his society is very traditional, but it seems like Lefi would have a more complex understand of what it means to be feminine or masculine. I liked the idea of the gender neutral, and the balance between masculine and feminine I would just have preferred a bit more nuance to those roles. The sex is nicely done, and different from anything I've read in other books. The biological differences feature, but it didn't feel like they were added just for sexual kink. The author did a good job creating a balance between both characters. It never felt like either was dominating or using the other. There were parts of this story that might have seemed cheesy, or overdone in a another story, but the author did a good job avoiding the truly flowery prose that would have taken it over the edge, and really bothered me.The mystery is really well thought out, and I like that the characters are thinking beyond the immediate issue to the larger implications, and starting to make plans about how best to confront that issue from many different angles. They don't forget what they have set out to do, but they don't let their objective blind them to what lies beyond that. It’s also not something they can fix on their own, and the secondary characters really play a large role in the solution.I really enjoyed Lefi's culture, and religion. It was nice reading about a people for whom sex is so natural, and basic. I was uncomfortable with the relationship between twins of differing genders, but there was nothing abusive, or demeaning about the bond. I loved the faith his people had, and their Goddess, and how their religion was about love, and acceptance not shame and fear. I really enjoyed this book, and hope to read more about this universe, and the people that populate it. I received a copy of this book through NetGalley in exchange for an honest review.