Professor van Dusen had just wrapped up three cases in Paris - the sensational Kinematograph murder, the sensational kidnapping of the Venus de Milo, and the outrageous Zola murder case. None of them were particularly difficult, he thought; but they had unfolded in such a short time, without a moment's pause, that even a criminological dynamo like the professor felt a certain need for rest. That’s why we made a brief visit to Biarritz. But as is typical for Professor van Dusen: hardly had we arrived when we found ourselves sliding right back into a case - what am I saying? Case is far too trivial: into one of the most incredible and dangerous adventures we have ever encountered. I mean the affair surrounding the jewel treasure of Empress Eugénie and the notorious supercriminal Monsieur Fantôme.