“This note,” he declared, “cannot constitute a proof against its author:  I mean an evident, material proof, such as we require to obtain from a judge an order of arrest.”

And, as Marius was protesting,

“This note,” he insisted, “is written with the left hand, with common ink, on ordinary foolscap paper, such as is found everywhere.  Now all left-hand writings look alike.  Draw your own conclusions.”

But M. de Tregars did not give it up yet.

“Wait a moment,” he interrupted.

And briefly, though with the utmost exactness, he began telling his visit to the Thaller mansion, his conversation with Mlle. Cesarine, then with the baroness, and finally with the baron himself.

He described in the most graphic manner the scene which had taken place in the grand parlor between Mme. de Thaller and a worse than suspicious-looking man,—­that scene, the secret of which had been revealed to him in its minutest details by the looking-glass.  Its meaning was now as clear as day.

This suspicious-looking man had been one of the agents in arranging the intended murder:  hence the agitation of the baroness when she had received his card, and her haste to join him.  If she had started when he first spoke to her, it was because he was telling her of the successful execution of the crime.  If she had afterwards made a gesture of joy, it was because he had just informed her that the coachman had been killed at the same time, and that she found herself thus rid of a dangerous accomplice.

The commissary of police shook his head.

“All this is quite probable,” he murmured; “but that’s all.”

Again M. de Tregars stopped him.

“I have not done yet,” he said.

And he went on saying how he had been suddenly and brutally assaulted by an unknown man in a restaurant; how he had collared this abject scoundrel, and taken out of his pocket a crushing letter, which left no doubt as to the nature of his mission.

The commissary’s eyes were sparkling,

“That letter!” he exclaimed, “that letter!” And, as soon as he had looked over it,

“Ah!  This time,” he resumed, “I think that we have something tangible.  ’A troublesome gentleman to keep quiet,’—­the Marquis de Tregars, of course, who is on the right track.  ’It will be for you the matter of a sword-thrust.’  Naturally, dead men tell no tales.  ‘It will be for us the occasion of dividing a round amount.’  An honest trade, indeed!”

The good man was rubbing his hand with all his might.

“At last we have a positive fact,” he went on,—­“a foundation upon which to base our accusations.  Don’t be uneasy.  That letter is going to place into our hands the scoundrel who assaulted you,—­who will make known the go-between, who himself will not fail to surrender the Baroness de Thaller.  Lucienne shall be avenged.  If we could only now lay our hands on Vincent Favoral!  But we’ll find him yet.  I set two fellows after him this afternoon, who have a superior scent, and understand their business.”