It is utterly fascinating and I highly recommend it, but one of the most interesting takeaways (consistent with this article) is that police officers quickly become utterly disillusioned with the integrity of the police department as an institution. They complain about unfair recruitment and promotion policies, injured officers who become "disposable", an emphasis on quotas instead of applying the law consistently, on politicization of policing priorities, and above all the city always settling cases against police misconduct so that accused officers never get a chance to clear their name in court, when innocent.
With this mindset, when they don't trust their own institution, the only people they trust are fellow officers -- not captains, not management, not the department, not the mayor. Which aligns with this article -- that Marines view the Marines as a trustworthy institution, while police don't see their own police department in the same light.
Now obviously police misconduct and brutality exist and are a huge problem. But the book very much opened my eyes to the idea that it's not only the behavior of police officers that needs better standards and accountability -- that treating police officers themselves better and more fairly may also be just as necessary to achieve full transparency and accountability. What if the "blue wall of silence" dissolved because police officers trusted their own institution, rather than just each other?