Legal World and Police Ranks
The French legal system is very much like the American one, although also different in some significant respects. In this book, all that matters is that there are notaires, who are essentially notary publics and who deal with wills (legalizing them and reading them), and avocats, who act as lawyers.
Regarding the police, the ranks are as follows:
gardien de la paix—roughly equivalent to a police officer
brigadier—roughly equivalent to a sergeant
capitaine—roughly equivalent to the US detective
lieutenant—the same as in the United States