Ancillary Sword ***mild spoilers to follow*** where Breq, the narrator, more-or-less proclaims that she's going to assassinate the Empress of the Galaxy (well, the Radch Empire that dominates human settlement of the galaxy). This was an exciting moment that seemed to promise that a somewhat contained story was going to escalate to a great adventure story. The rest of the book involves a trip to a throneworld that seems to cement that idea...and then the second book turned into a comedy of manners on and around out-of-the-way Athoek Station. I assumed that this was a diversion, a sort of mid-trilogy holding pattern while we wait for the big galaxy-shattering events of book 3...
Well, we're not done with Athoek Station by any stretch of the imagination, or the conflict-via-manners storytelling that came with it. In fact, this volume is so strongly tied to the previous one that they would have fit nicely into one volume. That also makes it hard to describe the plot without spoiling the previous book. Breq continues to navigate the Radch Empire's precarious politics, which are confused by the presence of Artificial Intelligence ships and also distributed/networked human intelligence. There is a bit more detail on the aliens around the Radchai, though they remain mostly mysterious. And, there is an action sequence to give the series something of a climax, though the solution once again depends more on Breq's clever diplomacy. And, if the action is slightly increased, the humor is much moreso. It's not too much of a stretch to say that the series, which started as space opera adventure, ends as a comedy.
Maybe it's not fair to speculate, but I get the impression that after her first novel, Leckie settled into a comfort zone telling this kind of softer, funnier character-based drama. It's worth it, however, because comfort and confidence also mean stronger writing. I don't think there's any question that this is the best written book in the series. The characters have really gelled, the humor works (something of a rare thing in serious science fiction), and the world only gets richer and more compelling even as we stay in such a narrow slice of it.
Though it's the best written of the trilogy, I'm not going to say it's the best. Ancillary Sword still benefits from introducing the ideas, the world, and the characters, and Mercy is hurt a bit by some of the false expectations set up by the first book - if we'd had this tone from the first, this would've been a more enjoyable read. Now that Leckie has found her voice, and it's a strong one, I'm interested to see what she'll do next (and she has the sweet bonus of winning all of the awards in the process of finding her voice).