Don Luis’s arrival caused great excitement.  The Prefect at once came up to him and said: 

“All our thanks, Monsieur.  Your insight is above praise.  You have saved our lives; and these gentlemen and I wish to tell you so most emphatically.  In my case, it is the second time that I have to thank you.”

“There is a very simple way of thanking me, Monsieur le Prefet,” said Don Luis, “and that is to allow me to carry out my task to the end.”

“Your task?”

“Yes, Monsieur le Prefet.  My action of last night is only the beginning.  The conclusion is the release of Marie Fauville and Gaston Sauverand.”

M. Desmalions smiled.

“Oh!”

“Am I asking too much, Monsieur le Prefet?”

“One can always ask, but the request should be reasonable.  And the innocence of those people does not depend on me.”

“No; but it depends on you, Monsieur le Prefet, to let them know if I prove their innocence to you.”

“Yes, I agree, if you prove it beyond dispute.”

“Just so.”

Don Luis’s calm assurance impressed M. Desmalions in spite of everything and even more than on the former occasions; and he suggested: 

“The results of the hasty inspection which we have made will perhaps help you.  For instance, we are certain that the bomb was placed by the entrance to the passage and probably under the boards of the floor.”

“Please do not trouble, Monsieur le Prefet.  These are only secondary details.  The great thing now is that you should know the whole truth, and that not only through words.”

The Prefect had come closer.  The magistrate and detectives were standing round Don Luis, watching his lips and movements with feverish impatience.  Was it possible that that truth, as yet so remote and vague, in spite of all the importance which they attached to the arrests already effected, was known at last?

It was a solemn moment.  Every one was on tenterhooks.  The manner in which Don Luis had foretold the explosion lent the value of an accomplished fact to his predictions; and the men whom he had saved from the terrible catastrophe were almost ready to accept as certainties the most improbable statements which a man of his stamp might make.

“Monsieur le Prefet,” he said, “you waited in vain last night for the fourth letter to make its appearance.  We shall now be able, by an unexpected miracle of chance, to be present at the delivery of the letter.  You will then know that it was the same hand that committed all the crimes—­and you will know whose hand that was.”

And, turning to Mazeroux: 

“Sergeant, will you please make the room as dark as you can?  The shutters are gone; but you might draw the curtains across the windows and close the doors.  Monsieur le Prefet, is it by accident that the electric light is on?”

“Yes, by accident.  We will have it turned out.”