There are a lot of nice touches in the book. The point of view of the characters switches at some point in the book, so if you get attached to certain characters, that might seem like a bummer. A mix of Alternate World and Apocalyptic destruction. The story is set around the League of Nations negotiations in France after WW1, where some of the participant are contacted by an enigmatic man who claims he has evidence of a lost civilization. They go off looking for it and the story progresses from there.
Tone is grim, perhaps a tad self-important, but great nonetheless.