The fifth Fractal Episode: Luna - https://www.amazon.co.uk/Luna-Fractal.../dp/B0CCKGFXVC

Retired Fleet Admiral, James Langsley, is called out of retirement to a secret meeting at the Moon colony. He is reunited with an old friend and a new enemy. Who will he choose to side with?

The Fractal episodes are standalone shorter works. You can read them in pretty much any order. They are a little introduction to the ongoing Fractal series.