Romance of the Underworld was adapted from a barnstorming stage piece by Paul Armstrong. Forced by circumstance into a life of sin and deprivation, Judith Andrews (Mary Astor) ends up as a "hostess" in a seedy dance hall. She is rescued by her kind-hearted employer Stephen Ransome (John Boles), and together the newlyweds carve out a new and decent life for themselves. Their happiness is threatened when a figure from their past, slimy racketeer Derby Dan Manning (Ben Bard), tries to blackmail the unfortunate couple. In a climax that would not have been possible in the Production Code-dominated 1930s, Derby Dan is foiled by sympathetic detective Burke (Robert Elliot), who slyly arranges for the villain to be bumped off by one of his own underworld buddies.
by Hal Erickson synopsis