The Art of Theft by Sherry Thomas (2020) Berkley Books

In which Charlotte Holmes, the pretend sister of the fictional Sherlock Holms, is seen through by a former friend of Mrs. Watson.  They embark on a dangerous mission to retrieve a particular piece of artwork that will be up for bid at auction.  The auction takes place in a chateau in France outside of Paris and has heightened security.  Which seems reasonable since it is owned by Moriarty.