The Lone Wolf - Louis Joseph Vance

The Lone Wolf is the first of eight books in a series featuring the jewel thief turned private detective Michael Lanyard. With his identity betrayed and the police on his heels, he must fly from Paris, which is made much more difficult by his self-imposed duty to take care of the beautiful Lucia, who has a dark secret of her own...A large number of movies have been based on the books. (Summary by Carolin and Wikipedia)