G-Men learn that "Brenda", notorious jewel thief, is heading for the US, to steal the Belgravian crown jewels currently on exhibit. The jewels are placed on a ship bound for Belgravia However, the guard is murdered and the treasures are stolen. Agent Dexter, alias Agent X-9, trails Blackstone, one of the gang members, who hides the jewels in a safe deposit vault of a bank. He takes the bank receipt to an art shop, where Marker, a paid accomplice, conceals it between an oil painting and its frame. Dexter arrests Blackstone and pursues Marker with the full intention of unmasking of the mysterious "Brenda"...
