This could be a polarizing book - it's a rich world that's not overly described, so often the reader is swept up in the currents of the gorgeous prose, not always having the time to know precisely what's going on. But really, the story concept is fairly simple: two agents who work across time and space for two opposing factions begin trading letters. What starts as a taunt becomes an almost affectionate correspondence. I became so invested in these shape-shifting, time-traveling loners who find each others' notes in birds' wings, tea leaves, tree rings, ashes... It's a poetic, surprisingly heartfelt story, and I got completely swept up. Come for the cool, speculative fiction concepts, stay for the absolutely gorgeous writing.