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 Beautiful 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 (Kenneth Griffith), a nasty, sniveling young scroat, who keeps blackmailing Heiss until he goes to far. The film ends in a London concert-hall where Margaret is playing the Mendelssohm Violin Concerto.