Behind the Mask (1946)

Lamont Cranston, aka the Shadow, has his hands full as the murder of blackmailing reporter Jeff Mann is blamed on him. Not only does the real murderer seem one step ahead of him as Lamont tries to discover his identity, but he is continually hampered from gaining crucial evidence by his jealous, interfering fiancée Margo Lane. Cranston perseveres and is rewarded with the clue he needs at one of Mann's victims' nightclubs.