Mary always said that most people didn't read the interleaved material and thought it was fantasy. If you read the entire book, you find out it's SF. There's really four layers of material:
1. The translations of the old documents.
2. The interleaved material which is email between the author/translator and his editor.
3. The person who found the translations with the interleaved material.
4. Us, actually reading.
The translations are from the 15th century, where an unknown land is fought over by people that are not in our history. The translator is sure this is new history, something that will bring him fame, particularly because the stories are about Ash, a female mercenary commander, and her exploits. But if you read the interleaved material, you find things are not quite what they seem.
I usually have trouble reading battle text and just skim or skip, but Mary made me sit partly up in bed, pulled by the words. Not just the short phrases and rhythm, but the way the words moved with each other. This has never happened before. The entire book pulled me along and I happily started Book 2 last night.