The Uncatchable Mr. Frederic (1946)

A novelist has created "L'Inssaisissable Frederic" ,some kind of "Gentleman Cambrioleur" such as Arsene Lupin,who loves to steal on the trains (when they enter tunnels) or in the station.He 's got fine techniques and many ways of stealing ,for instance taking a cast of a wealthy English lady's hand (to latch onto the woman's valuable ring). Enter BB alias Richard .His motto might be: "theorizing is all very well ,but..." Pretty soon,Frederic will not be an imaginary character anymore ...for the novelist's ideas are pretty good.