“Mademoiselle is innocent of the knowledge of any of these things,” Louis declared earnestly.  “She is a very charming and a very beautiful young lady, but if ever a young lady needed friends, she does!”

“Why is she here at all?” I demanded.  “Why was she not left behind in Paris?  If there is no part for her to play in this little comedy, it seems to me that she would have been much better out of the way.”

“Captain Rotherby,” Louis said, “there was a reason, and some day you will understand it—­why it was necessary that she should come to London with her uncle.  I can tell you no more.  You must not ask me any more.”

I looked into Louis’ impenetrable face.  I could learn nothing there.  His words had left me partly unconvinced.  Somehow I felt that the only time he had spoken the entire truth was when he had spoken of Felicia.  Yet it was certainly true that I owed these people something, and I had no wish to shrink from paying my debt.

“Tell me,” I said, “if I take Delora’s place to-night, and if your scheme is successful, does that free him?  Will he be able to come back?  Will it be for the benefit of mademoiselle?”

“But most certainly!” Louis answered earnestly.  “It is not an organization against which we fight.  It is one or two desperate men who believe themselves robbed.  Once they are out of the way, Delora can walk the streets a free man.  There would be nothing,” he added, “to prevent your seeking his friendship or the friendship of his niece.”

“Very well,” I agreed.  “I will spend the night in Mr. Delora’s rooms.  I shall leave it to you to make all the arrangements.”

Louis looked at me with a curious expression in his face.

“You understand, monsieur,” he said slowly, “that there may be danger?”

“Naturally I understand,” I said.  “If it comes to a fight, I shall be prepared, and I have had a little experience.”

“However well armed you may be,” Louis said, “there will be a risk.  Our enemies are swift and silent.  One of them, at any rate, is an accomplished criminal.  They are too clever for us unaided.  I could take Mademoiselle Delora to Scotland Yard to-day, and I could tell them what we fear.  They might patrol the hotel with the police, and even then you would wake in the night and find some one by your bedside.”

“By the bye, Louis,” I said, “why all this mystery?  According to you, Delora is an honest man.  Why don’t you go to the police?”

Louis shook his head.

“We are not free to do that,” he said.  “Delora is honest, but it is a great secret which he controls, and the only chance of using it successfully is to keep it a secret from the whole world!”

“How am I to be introduced into the room, Louis?” I asked.

“That,” he answered, “will be easy.  There are two lifts, as you know,—­one from the smoking-room and one from the entrance hall.  The number of Mr. Delora’s apartment is 157.  Here, by the bye, monsieur, is a key.”