I picked up this book because I'd heard good things about the author, and was not disappointed.
The novella consists mostly of letters between two friends: one newly made Emperor, and the other out to quash a rebellion for him. It's a short book, but packs quite a punch; as with many epistolary novels, there's more unwritten than actually on the page, which makes for wonderfully thought-provoking reading. And unlike in most epistolary novels I've read, the letters here actually sound like letters that people might write to one another: there's not a lot of scene-setting, description, dialogue, or telling each other what they already know, which leaves us to fill in a lot of blanks.
Like many of my favorite books, this one is set in a secondary world, but without magic, dragons and so on. It focuses on political intrigue and the corrupting effects of power, and is predictably grim. The one problem I found was that the language felt perhaps too modern and slang-y for the (ambiguous, but certainly premodern) setting. Purple and Black is expensive (I was fortunate enough to find it at the library) but was certainly worth an evening of my time.