Spirou and Fantasio, in transit through Paris airport, are kidnapped by French counter-intelligence: in exchange for the release of two French nationals from Soviet prisons, the KGB demanded the two reporters' assistance. Because Moscow has a problem: the mob is getting increasingly more powerful and bold, and it has infiltrated the authorities so thoroughly they can't fight back anymore. They do know, however, that the big boss is someone Spirou and Fantasio have met before and simply cannot ignore.