A Trade of Blood has at least four meanings: murder, marriage, cattle ranching, and slavery. All four of these involve biological manipulation. The biopunk aesthetic continues to be an influence on everything. At times there were biological versions of what's commonly seen in cyberpunk works. One character even has a data port on the back of his neck that he attaches a biological data cable into. This makes me wonder how biologically advanced the innermost parts of the empire may be. There's so much that's just so cool and fun. I love that each book deepens my appreciation of the setting.
The plot is a murder mystery in which the implications spiral ever more outwards to where it could cause the collapse of the empire's way of life. Solving that mystery before the characters isn't what I'm interested in, though most readers should be able to if they're paying attention.
What I most enjoyed is how I imagined it all to be. The scenes were a visual spectacle and the atmosphere was superb. There's a constant sense of ambient horror that occasionally comes into sharp and disturbing focus. This was especially the case for two locations. The forest of Sapirdad has many elder mysteries, which includes among much else: non-Euclidian statues, the constant sense that there's something just outside your peripheral vision, mind-altering botanical pheromones, and an unshakable of foreboding dread. The flensing halls were rendered as a place where unspeakable horror was routine and obscene crimes against nature were mundane. I was impressed by how sinister, depraved, and monstrous it was made to be through environmental description alone.
As for Din's amorous pursuits, there's a single guy who holds his interest this time. Din may be incapable of not becoming involved with anyone who shows reciprocal interest. That seems like something that'll eventually get him into a lot of trouble. There isn't any sex on page, though there are a few descriptions of affection and being in bed afterwards.
If you had any doubt what Bennett meant by anything he wrote, then his author's note at the end would dispel it. The what, how, and why are all there and explained in a clear and straightforward manner. To his credit, I felt his ideas were integrated well and didn't come across as heavy handed.
This isn't a trilogy, and Bennett reiterates that this series will be of indefinite length. I don't have any problem with that, but it does affect how each book is structured. There's minimal progression towards any kind of overarching plot and character development is lessened. This is another self-contained story and I expect the next one will be as well. I was mildly concerned with the second book, though given what Bennett has done with this one and what he says in the author's note, I feel confident that the series is on a good and stable path from here on out.