So I was searching for something on Google today and found one of my own old websites from 2006, Secrètes de Paris (the spelling was on purpose, I thought it was funny at the time). I didn’t realize it was still online, and started looking through the posts and found this photo of Deluc Detective Agency. Everyone in Paris already knew about this place (hard to miss the green neon right by the Louvre) before it became internationally famous in Woody Allen’s latest film, Midnight in Paris. So yes, there really is a Deluc Detective Agency in Paris, at 18 rue du Louvre.
This is also the location of the Aimee Le Duc detective agency from Cara Black's Paris series. Her agancy is located on Rue de Louvre on the second floor. I assume that De Luc is the inspiration for thaat!