Descius Heiss is a French expatriate, and former Devil's Island prisoner, with two passions; driving shrewd bargains in antiques at his Sly Corner Shop, and the care of his motherless, violin-playing daughter, Margaret. But, his comfortable wealth comes more from being a fence for stolen goods than it does buying-and-selling antiques. His secret is discovered by his shop assistant Archie Fellowes, a nasty, sniveling young rat, and he begins blackmailing Heiss. Heiss employs the usual solution to blackmailers, and the film ends in a London concert-hall where Margaret is playing the Mendelssohm Violin Concerto.