Double Danger (1938)

Robert Crane is a slick jewel thief who also doubles as a novelist writing about a slick-jewel-thief known as 'The Gentleman,' who the police have never been able to catch. Although Police Inspector Davd Theron, a friend of the 'novelist' Crane, suspects Crane may be the thief he writes about, he has never been able to prove it. Theron sets a trap for Crane, but jewel-thief Carolyn Martin gets there first.