Willy Vanderbrook, a brilliant French Belgian who has become a citizen of the world, is approached about the job of concierge at one of Paris's great 5-star hotels.
He is welcomed by Serge Luyperts, a childhood friend, a blasé café owner who has taken in his ex-brother-in-law Frank Vrut, a Walloon separatist who is slightly psychopathic. Willy's application - rejected because he's too Belgian - forces him and his compatriots to carrying out a ridiculous and "royally" vengeful deception.
By pretending to be heir to the Belgian throne, Willy and his gang set off a series of joyful events in the 5-star establishment, which quickly grab the attention of Jessica, a professional schemer. She thinks she's seducing the future King of Belgium, but she has in fact met a craftier person than herself.
This burlesque detonator then drags the "Made in the Flat Country" trio into a scam with more far-reaching and dangerous consequences.