Arsène Lupin, Gentleman-Thief (Arsène Lupin #1)

Who is this mysterious Arsène Lupin? He keeps announcing his upcoming appearance in the homes of very rich people to steal their possessions, and he is seemingly able to do the thievery without any trace of his entering or leaving. He steals only from the very, very rich. How is he able to do it?

Arsène Lupin is a classic mystery novel in France. It's on the list of the 1001 Children's Books You Must Read.