“Ah! then that changes the aspect of things which no longer corresponds with Monsieur Rouletabille’s ideas!” cried Monsieur de Marquet. “If that key never left Mademoiselle Stangerson, the murderer must have waited for her in her room for the purpose of stealing it; and the robbery could not have been committed until after the attack had been made on her. But after the attack four persons were in the laboratory! I can’t make it out!” “The robbery,” said the reporter, “could only have been committed before the attack upon Mademoiselle Stangerson in her room. When the murderer entered the pavilion he already possessed the brass-headed key.” “That is impossible,” said Monsieur Stangerson in a low voice. “It is quite possible, Monsieur, as this proves.” And the young rascal drew a copy of the “Epoque” from his pocket, dated the 21st of October (I recall the fact that the crime was committed on the night between the 24th and 25th), and showing us an advertisement, he read:— “‘Yesterday a black satin reticule was lost in the Grands Magasins de la Louvre. It contained, amongst other things, a small key with a brass head. A handsome reward will be given to the person who has found it. This person must write, poste restante, bureau 40, to this address: M. A. T. H. S. N.’ Do not these letters suggest Mademoiselle Stangerson?” continued the reporter. “The ‘key with a brass head’—is not _this_ the key? I always read advertisements. In my business, as in yours, Monsieur, one should always read the ‘personals.’ They are often the keys to intrigues, that are not always brass-headed, but which are none the less interesting. This advertisement interested me specially; the woman of the key surrounded it with a kind of mystery. Evidently she valued the key, since she promised a big reward for its restoration! And I thought on these six letters: M. A. T. H. S. N. The first four at once pointed to a Christian name; evidently I said Math is Mathilde. But I could make nothing of the two last letters. So I threw the journal aside and occupied myself with other matters. Four days later, when the evening paper appeared with enormous head-lines announcing the murder of Mademoiselle Stangerson, the letters in the advertisement mechanically recurred to me. I had forgotten the two last letters, S. N. When I saw them again I could not help exclaiming, ‘Stangerson!’ I jumped into a cab and rushed into the bureau No. 40, asking: ‘Have you a letter addressed to M. A. T. H. S. N.?’ The clerk replied that he had not. I insisted, begged and entreated him to search. He wanted to know if I were playing a joke on him, and then told me that he had had a letter with the initials M. A. T. H. S. N., but he had given it up three days ago, to a lady who came for it. ‘You come to-day to claim the letter, and the day before yesterday another gentleman claimed it! I’ve had enough of this,’ he concluded angrily. I tried to question him