This is the second book in the author's Winnowing Flame series, following on from The Ninth Rain (which I absolutely loved) and it keeps the tension and action ticking over nicely even as all sorts of bombshells are dropped on our protagonists.
It's really difficult to talk about what happens in this book without spoiling the first one, so I won't go into massive details about it. It pretty much carries on straight from the end of the previous book - we know now that Hestillion was effectively aiding the enemy even though she didn't realise it, and in The Bitter Twins she spends the entire time as their captive. The war-beast pod she stole has hatched and she is effectively torn between her need to keep that creature safe and the realisation that she has betrayed her people completely.
Meanwhile, back in what is left of Ebora, our other protagonists are trying to find allies against their common enemy and fight its incursions with limited resources. Tor and Noon go off on what looks like being a wild goose chase, in search of information that might help the war-beasts remember their connection to their previous lives, and discover some long-held secrets about the Eborans. Theirs is the main story, with what Bern and Aldasair get up to in the meantime proving to be more of a B plot.
Another excellent book, can't wait to see how this series finishes off. The final book (The Poison Song) is due out May next year!