“Proofs?  Why, we don’t need them!  They’re here.  M. Fauville himself supplies them:  ‘The end is at hand.  I can see it in her eyes.’  ‘Her’ refers to his wife, to Marie Fauville, and the husband’s evidence confirms all that we knew against her.  What do you say, Chief?”

“You’re right,” replied Perenna, absent-mindedly, “you’re right; the letter is final.  Only—­”

“Only what?”

“Who the devil can have brought it?  Somebody must have entered the room last night while we were here.  Is it possible?  For, after all, we should have heard.  That’s what astounds me.”

“It certainly looks like it.”

“Just so.  It was a queer enough job a fortnight ago.  But, still, we were in the passage outside, while they were at work in here, whereas, this time, we were here, both of us, close to this very table.  And, on this table, which had not the least scrap of paper on it last night, we find this letter in the morning.”

A careful inspection of the place gave them no clue to put them on the track.  They went through the house from top to bottom and ascertained for certain that there was no one there in hiding.  Besides, supposing that any one was hiding there, how could he have made his way into the room without attracting their attention?  There was no solving the problem.

“We won’t look any more,” said Perenna, “it’s no use.  In matters of this sort, some day or other the light enters by an unseen cranny and everything gradually becomes clear.  Take the letter to the Prefect of Police, tell him how we spent the night, and ask his permission for both of us to come back on the night of the twenty-fifth of April.  There’s to be another surprise that night; and I’m dying to know if we shall receive a second letter through the agency of some Mahatma.”

They closed the doors and left the house.

While they were walking to the right, toward La Muette, in order to take a taxi, Don Luis chanced to turn his head to the road as they reached the end of the Boulevard Suchet.  A man rode past them on a bicycle.  Don Luis just had time to see his clean-shaven face and his glittering eyes fixed upon himself.

“Look out!” he shouted, pushing Mazeroux so suddenly that the sergeant lost his balance.

The man had stretched out his hand, armed with a revolver.  A shot rang out.  The bullet whistled past the ears of Don Luis, who had bobbed his head.

“After him!” he roared.  “You’re not hurt, Mazeroux?”

“No, Chief.”

They both rushed in pursuit, shouting for assistance.  But, at that early hour, there are never many people in the wide avenues of this part of the town.  The man, who was making off swiftly, increased his distance, turned down the Rue Octave-Feuillet, and disappeared.

“All right, you scoundrel, I’ll catch you yet!” snarled Don Luis, abandoning a vain pursuit.

“But you don’t even know who he is, Chief.”