An international gang of thieves and swindlers decide to move their criminal operation to the Teutonic city of Cologne, but Tom Wilkens, one of the best agents of the international police, is not far behind and leads an investigation to unmask the criminals.

Harry would prefer to marry his Grete on the spot, but at first he must have the approval of his father-in-law. He must prove that he is able to feed his future wife. So the poor fellow has a lot to think about in order to make enough money - which does not go without complications.