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In chapter one of Universal's G-Men serial Secret Agent X-9, the government learns of the death in Hungary of Victor Brenda, the world's most daring jewel thief. But Dexter (Scott Kolk), Agent X-9, believes the rumors of Brenda's demise to be premature, especially after learning that Blackstone (Henry Brandon), the master criminal's finger man, has arrived in the United States. X-9 assigns one of his young colleagues, Jimmy Tilton (Robert Dalton), to safeguard the return of the famed Belgravian crown jewels, but Brenda has Jimmy murdered in his stateroom and the treasure vanishes into thin air. A trail, however, leads X-9 to an art shop where he interrupts mysterious Shara Graustark (Jean Rogers) and Marker (Max Hoffman, Jr.), one of Blackstone's henchmen. A speedboat chase ensues, during which X-9 is knocked unconscious. As chapter one concludes, the runaway boat crashes into a huge buoy.