One of the books I've pre-ordered this year, Raven Stratagem is the sequel to last year's Ninefox Gambit, which I really enjoyed and hope will win this year's Hugo for Best Novel (it's got my vote, at least!). As with most series, this book will make much more sense if you've read the first one, particularly as the action continues pretty much straight from the events at the end of the previous book.
In short, our main character Kel Cheris, a mathematically-inclined infantry captain, has ended up as the host for the consciousness of a long-dead general who went a bit crazy and killed many of his soldiers. Since he (Jedao) is a tactical genius, the decision was made to use newly-invented technology to preserve his consciousness and bring it out when needed, the most recent occasion being to deal with a bunch of heretics on a space station.
In the wake of that, which forms the bulk of the events of Ninefox Gambit, Cheris uses her status to take over a small fleet of ships and attempt to both deal with an invasion and set into motion Jedao's plan to overturn the whole system. The main driver for this is what is called 'formation instinct', the mental conditioning that the military faction use to ensure obedience to orders - some soldiers already have problems with this and therefore obey orders because they choose to, while most have no choice. Meanwhile there is also a lot of maneuvering going on in the other factions as the possibility of immortality is dangled in front of their respective leaders, so we also spend a lot of time with the Shuos leader and his various issues.
In some ways, this feels like a more accessible book than Ninefox Gambit and more of a traditional space opera. By the end of it, in preparation for the next book in the series (which I understand is called Revenant Gun, a slightly ominous name since that technology is directly-related to Jedao), Cheris has put her plan into action and everyone is going to be dealing with the fall-out. Those who are still alive, of course! Enjoyed it very much, can't wait to see what happens next...