This book is really the story of why and how IEX was created. Humans made bad decisions. So, to protect people from other people, we moved the operation of the stock market to being run by computers. The natural consequence was for people to game the system with computer code. Rather than stay vigilant against new exploitations, we just redefined fair. The team behind IEX created it to eliminate these problems and establish a fair place for trading to occur.
About halfway through the book, I watched a commercial where an investment company touted their guaranteed one second trades. To the average person, this probably sounds amazing. The thing is that companies like this operate in milliseconds (1/1,000) and nanoseconds (1/1,000,000). Plus, they operate Dark Pools where the trade is obfuscated from independent review. Your trade could get executed where it benefits them and not you.
The overarching theme is that complexity and obfuscation created an environment where bad things can happen. As a technologist in education, I fight against this every day. We desire simplicity. Yet every change and especially those we execute without a good understanding of the business case creates complexity which will result in a failure. When no one fully understands how all the components work together, it exists to fail. Funnily enough, my team, the database administrators (really application administrators) sit at the intersection of the analysts, vendors, operating system admins, storage admins, network admins, and others. So this is familiar territory.
Zoran Perkov and Sergey Aleynikov are unsung heroes I am sure about whom I will spend more time reading.