This is the second Aimée Leduc book for me; Aimée is the half French, half American private investigator who lives in Paris and foils evildoers at the highest levels. The author is very specific about location and has a map in the front of the book so you can see where everything occurs.
The Marais is the old Jewish quarter of Paris; the murder victim is an old Jewish woman who is marked after death with a swastika on her forehead. The event is tied to a murder committed when the Nazis occupied Paris and people did anything for food. The story is a complicated one, mainly told as a recounting of what the very athletic and exhausting Aimée did, but with occasional chapters told from the viewpoint of various characters.
Aimée's agency, run with her partner Renée, who is a dwarf, usually focuses on computer security. This was the first in the series, published in 1999, set in 1993. I was surprised at the sophistication of the hacking aspect of the story, though I certainly didn't have a clear idea what many of the terms used actually meant.