I have to say, I was immensely glad to see that when the UK version of this book was due out, the cover was different from the US one - that not only has a slightly different title (The Traitor Baru Cormorant) but features a porcelain mask shaped like a human face. And while masks do play an important part in one of the cultures involved in The Traitor, that cover is horribly reminiscent of a whole tranche of lookalike YA books currently on the market; all it needed was a winsome teenage girl in a prom dress looking wistfully back over her shoulder...
Anyway, on to The Traitor.
Baru Cormorant (hence the US title) is born on the island of Taranoke, which is in the process of being taken over by the forces of the Masquerade, who impose their way of doing and thinking with ruthless efficiency. They certainly don't like the fact that many Taranoke men are openly in relationships with other men, let alone that there are families like Baru's, with two fathers and one mother. Seeing that the ascendancy of the Masquerade is imminent, even as a child, Baru decides that the best way to fight them is from within and when she is head-hunted for their school, she engages with them wholeheartedly. Her view is that she must learn to use the weapons the Masquerade use, which are things like money and ways of thinking, though these are often backed up by weapons if necessary. Once she has learned enough, she can help her own land be free of their influence once more.
As an adult (if barely so) she is given the job of Imperial Accountant for the conquered province of Aurdwynn, which is ruled by a patchwork of dukes. They are what is left of that country's nobility after a botched attempt at rebellion fifteen years earlier and part of Baru's job is a) to survive longer than her two predecessors and b) figure out whether any of the dukes are cooking their ledgers to cover up a potential second rebellion. As she gets to know the people of Aurdwynn, Baru herself becomes involved in their plans for revolt and eventually becomes its ringleader, a figurehead for the people to rally behind who is seen to be one step removed from the dukes, who are all in it for themselves.
While there are elements of the classic 'grimdark' fantasy here, The Traitor doesn't feel quite as grim and depressing as some of those books can be - it's been my experience that authors sometimes seem to do bad things to characters in the most gruesome manner for shock value as much as anything. A flaw for me, in the storytelling, is the amount of detail given to plotting out the actions of the various battles that take place, which I think probably didn't need to be quite as spelled out all the time. There is, of course, more going on than meets the eye and Baru is not the only one who surprises people with her choices as she goes along.
I'm not sure if this is a standalone, because it certainly teases for future books in this setting at least, but it certainly can be read as one.