Neptune’s Brood is a great space opera about interstellar banking by Charles Stross. Seriously great.
The protagonist, Krina Alizond, is a banking historian who now that she’s worked her way out of her indentured servitude to the hugely wealthy intelligence that created her, is into Ponzi schemes and especially how they play out over huge distances and slower than light travel. There are tonnes of digressions into the history of banking and how to set up a colony around another star when you can only travel at a percent of the speed of light and building a ship to do that is planetary economy expensive. The solution is debt and repayment over the long long term.
Alizond, is also interested in what happened to her sibling (who was also forked off of the same hugely wealthy being) on a distant world so she’s going there by hitching a ride working on a chapel-ship dedicated to the Fragile (ie humans who have not been upgraded to actually function in space and over the timescales one needs to be thinking in if you want to make a difference in a huge uncaring universe). There are banking privateers and mermaids and queens and a (really boring) space battle. It’s set in the same universe as Saturn’s Children, but I haven’t read that one and it did not matter at all.
Definitely one of my favourite books of the year, and it even includes an epigraph from David Graeber’s Debt: The First 5000 Years (one of my favourite nonfiction books). If you like thinking about how things could be if they were different, this is a book you should read. We have science fiction basically so books like this can be made.