Superior to similar movies like Serpico or Donnie Brasco, POTC deals with a NYC detective who decides to blow the whistle on some major wrongdoing...provided his friends/family are not part of the deal. What seems simple and clearcut in the beginning becomes murky, twisted, and protracted as time wears on. Ethical issues and sacrifices cause widespread suffering. This film is superbly written and cast. I don't think Treat Williams ever got another role as heart stopping and wrenching as this one. Lindsay Crouse is magnificent as his supportive wife. Cinematography reinforces the emotional impact of the story--watch early on the scene with Treat chasing junkies in the rain. The misery of it just breaks your heart and you can see how, without a do-gooder leader in charge of a police force, it would be easy for these detectives to see themselves as princes of the city. This film delivers a wallop, and about midway, you'll feel like having a drink and a tranquilizer. Lumet was a master.