The two major characters are Zoé and Nico. Zoé is a young girl who has been silent since her policeman father was killed - her mother is also with the city police department. Nico is a cat burglar, who's connected to Zoé by the cat they share (although neither of them knows it). The cat lives with Zoé during the day, and goes with Nico on his burglaries at night. Zoé's and Nico's lives get tangled together when Zoé follows the cat to find out where it goes at night - and Nico's adventures take her too close to the violent criminal who killed her father.
The run-time is very short at 65 minutes (including the credits). I didn't much like the style of animation (blocky and scratchy), but some critics love it so that's very much a matter of personal taste. However, I'm definitely acquiring a taste for French animated kids' movies (see also "Phantom Boy" and "My Life as a Zucchini"). They retain the North American habit of making villains less threatening than they would probably be in real life, but they dispense entirely with "cutesy" and also tend to address things from a more mature viewpoint than would be expected in an American kids movie.
I didn't like the animation ... but I enjoyed the story and characters quite a bit.