This story is richly populated with believable and distinct aliens, and even more unusually, with believable interactions between aliens, and between aliens and humans. Once things get into gear, that richness thoroughly draws you in to lose yourself in the story. Unfortunately, before that happens, it can be a bit maddening to read because of too many elliptical and unexplained references, undoubtedly related to the prior books' events. A lot of them are minor - such as nicknames certain characters use for each other - but they still pull you out of the story.

Dr. "Mac" Mackenzie Connor wants nothing more than life as a biologist passionately studying salmon. Unfortunately, despite her claims and wishes to the contrary, events have made her a very important person at the focus of present interspecies conflicts. Mac is in company with her friend Emily, whose physical destruction at the hands of the alien Ro has been repaired, but the mental repairs look more like a matter of glaze applied over something with lots of highly visible cracks. Mac wants to get Emily away to heal among other humans doing what she wants, but instead, places them all directly in the path of the Ro's next move and a handful of other interspecies conflicts, the ultimate aim of which may involve the complete devastation of Earth itself - a devastation that more than one species may have planned for more than one way of filling that imperative to survive.

This is a great, intense read about the different ways life develops and how different species interact. Fascinating for someone interested in interactions between humans and aliens who are not stereotypical bug eyed monsters. The author's training as a biologist shows, even when she's not talking of species she's studied from life. An enjoyable read, but because of the way it is written, I would strongly recommend reading Survival and Migration, the prior books in the series, first.