Arsène Lupin goes undercover, wearing disguises, to locate a well hidden crystal bottle stopper. He also has to figure out what makes that particular bottle stopper valuable.

The Minister and the Prefect of Police call on a policeman stationed in Africa, Victor.

The Château de Tornbull has gradually become a center of feverish tourist activity, which deeply upsets Stefan, the young Count of Tornbull, the landlord of the estate. All the more as among the visitors prowls around an uncanny individual, who seems to covet the precious paintings in which the Tornbull family takes so much pride...

Arsène Lupin meets his author 'Maurice Leblanc (II)' in this story taking place in Brussels, Belgium and dealing with a blackmail about love letters.