I have heard a number of people wonder what it would be like to go back in time with high caliber automatic weapons and change the course of history, but it was not until I read Athenian Steel that I understood that P.K. Lentz had taken that same question of WHAT IF? to a much higher level than anyone has before.
Alternative history typically changes a single major outcome, like the victor of a strategic war, such as WWII and sets a story in that alternative setting. Lentz throws caution to the wind, having augmented meta-humans from thousands of years in our future, visit Athens during the Peloponnesian War. The meta-humans can pilot a ship through layers of reality. I want to do that too! Changing history in one layer does not translate to another, or does it?
One meta-human, named Geneva, purposefully strands herself in a layer, in ancient Athens on a mission. Two others are stranded somewhere on that world. Geneva, she is physically perfect, a living weapon, a computer, knows everything that will happen before the Greeks or the Spartans. She will get involved, muck with history, and change human technological advancements, but at what cost?
Lentz is such an intelligent author. The way he introduces Geneva and her abilities. The different acceptance of her by the Spartans and the Greeks. Her goals versus the goals of each city state. Her goals versus those of the other meta-humans. The fact that she IS fundamentally human, with emotional needs and wants resonates throughout the entire book.
His characters are human, complex and credible. Everyone is damaged, has problems, can't get out of their own way, or are nasty. You can understand them all.
Each change made in history will have downstream ramifications, some instrumental in creating a wholly new path for mankind. You can't predict the outcome of most of the choices made, and that is where Lentz starts having fun.
His knowledge of this area of history is prodigious. It is detailed, but doesn't get in the way of the plot. There are no big blocks of exposition, no info-dumps to define historical terms, culture or battle. This is a fast moving adventure.
You just have to read it to believe it...