The book provides an in-depth overview of how modern financial markets came to be, the different markets, players, and technologies at play, and clarification of what both sell-side and buy-side professionals do daily (with a far greater emphasis on the sell-side); all of this, from the perspective of someone who entered the field as a technical/quantitative professional. It's written with so much depth and care as if to serve as a guide for what he had wished to have had when he first entered the finance industry.
The author (Alex) was a Physics PhD who had entered the financial industry with no prior experience. By his admission, he got in during a time when the financial industry was just looking for anyone with an advanced degree to create advanced financial models.
Today that landscape has completely changed. At the time of writing which I presume to be in the mid-2000s, he realized the influx of gifted individuals with great technical aptitude who didn't quite understand the industry they were entering.
He starts the book on an expository note detailing the formation of modern equity and debt markets, the various players and institutions, and a day-to-day look at what the financial industry looked like at the time. So in-depth is this intro he describes the major financial hubs (at the time of writing) and their reason for being.
I found myself thinking "Billions wasn't too far off".
He goes on to write about the various economic factors and institutions that affect the markets and subsequently the various security markets. While I did read over these chapters of the second part I found the first few on the macroeconomic factors, yield curve, and interest rates to be by far the most important. Readers can skip to chapters and subsections they find relevant, and the book is structured to account for this reading style.
Finally, he talks about the various "technical" aspects a technical individual might be brought into a firm to solve as well as an in-depth look at what it looks like in practice(Mostly software and systems plumbing).
If the next few years are as uncertain as they are likely to be due to the increasing generality of proficiency of AI systems, I think Alex generally (indirectly) provides an enlightening case for why that might be a profession of choice for those trying to hedge against the future. It's pretty close to the core of what drives a lot of modern society and quite obviously, the one thing that keeps it all moving. Money.