In December 1925, a group of Hungarian nationalists were caught trying to put into circulation a large quantity of counterfeit francs in a bid to weaken the French economy and fund irredentist action in Central Europe. This article uses this plot and police investigations to examine the central role of counterfeiting in international crime control and policing in interwar Europe and to make broader claims about interwar internationalism. Earlier Hungarian plots targeting neighboring states’ currencies had paved the way for the founding of the International Criminal Police Commission, today known as Interpol, and prompted European jurists to develop ideas about international criminal law. France initially used its investigations in 1925 as a tool of power politics, hoping to reshape the political order in Central Europe. Once this effort failed, France sought other means to assert authority in Europe, appealing to the League of Nations to draft an international convention on counterfeiting. The resulting convention laid the institutional and ideological bases for an expansion of international policing and law in the 1930s. The counterfeiting plot reveals the shifting power relations in 1920s Europe and points to the interconnections between ‘utopian’ internationalism and ‘realist’ security concerns on the continent.