When you want an agent to penetrate an enemy-occupied country and stay free long enough to do a tricky job, you need someone who's used to getting around without attracting attention. Who better than a man who smuggled diamonds in and out of that very country for years?
But there's a difference between peace-time and war. Before, the worst that could happen to him was to be put in jail. Now, if he was caught, he faced certain death!