Mlle. Levasseur did not leave the house during the afternoon.  In the evening Don Luis ordered Mazeroux’s men to follow any one who might go out at that time.

At ten o’clock the sergeant joined Don Luis in Hippolyte Fauville’s workroom.  Deputy Chief Detective Weber and two plain-clothesmen were with him.

Don Luis took Mazeroux aside: 

“They distrust me.  Own up to it.”

“No.  As long as M. Desmalions is there, they can do nothing against you.  Only, M. Weber maintains—­and he is not the only one—­that you fake up all these occurrences yourself.”

“With what object?”

“With the object of furnishing proof against Marie Fauville and getting her condemned.  So I asked for the attendance of the deputy chief and two men.  There will be four of us to bear witness to your honesty.”

They all took up their posts.  Two detectives were to sit up in turns.

This time, after making a minute search of the little room in which Fauville’s son used to sleep, they locked and bolted the doors and shutters.  At eleven o’clock they switched off the electric chandelier.

Don Luis and Weber hardly slept at all.

The night passed without incident of any kind.

But, at seven o’clock, when the shutters were opened, they saw that there was a letter on the table.  Just as on the last occasion, there was a letter on the table!

When the first moment of stupefaction was over, the deputy chief took the letter.  His orders were not to read it and not to let any one else read it.

Here is the letter, published by the newspapers, which also published the declarations of the experts certifying that the handwriting was Hippolyte Fauville’s: 

“I have seen him!  You understand, don’t you, my dear friend?  I have seen him!  He was walking along a path in the Bois, with his coat collar turned up and his hat pulled over his ears.  I don’t think that he saw me.  It was almost dark.  But I knew him at once.  I knew the silver handle of his ebony stick.  It was he beyond a doubt, the scoundrel!

“So he is in Paris, in spite of his promise.  Gaston Sauverand is in Paris!  Do you understand the terrible significance of that fact?  If he is in Paris, it means that he intends to act.  If he is in Paris, it means certain death to me.  Oh, the harm which I shall have suffered at that man’s hands!  He has already robbed me of my happiness; and now he wants my life.  I am terrified.”

So Fauville knew that the man with the ebony walking-stick, that Gaston Sauverand, was designing to kill him.  Fauville declared it most positively, by evidence written in his own hand; and the letter, moreover, corroborating the words that had escaped Gaston Sauverand at his arrest, showed that the two men had at one time had relations with each other, that they were no longer friends, and that Gaston Sauverand had promised never to come to Paris.