"Suppose Daubrecq returns?"

"If he returns, that will be so much the better: we shall have him."

"And, if he only passes?"

"In that case, the Growler and the Masher must follow him."

"And if they lose sight of him?"

Lupin did not reply. No one felt more than he how fatal it was to remain inactive in a hotel bedroom and how useful his presence would have been on the battlefield! Perhaps even this vague idea had already prolonged his illness beyond the ordinary limits.

He murmured:

"Go now, please."

There was a constraint between them which increased as the awful day drew nigh. In her injustice, forgetting or wishing to forget that it was she who had forced her son into the Enghien enterprise, Mme. Mergy did not forget that the law was pursuing Gilbert with such rigour not so much because he was a criminal as because he was an accomplice of Arsene Lupin's. And then, notwithstanding all his efforts, notwithstanding his prodigious expenditure of energy, what result had Lupin achieved, when all was said? How far had his intervention benefited Gilbert?

After a pause, she rose and left him alone.

The next day he was feeling rather low. But on the day after, the Wednesday, when his doctor wanted him to keep quiet until the end of the week, he said:

"If not, what have I to fear?"

"A return of the fever."

"Nothing worse?"

"No. The wound is pretty well healed."

"Then I don't care. I'll go back with you in your car. We shall be in Paris by mid-day."

What decided Lupin to start at once was, first, a letter in which Clarisse told him that she had found Daubrecq's traces, and, also, a telegram, published in the Amiens papers, which stated that the Marquis d'Albufex had been arrested for his complicity in the affair of the canal.

Daubrecq was taking his revenge.

Now the fact that Daubrecq was taking his revenge proved that the marquis had not been able to prevent that revenge by seizing the document which was on the writing-desk in the study. It proved that Chief-inspector Blanchon and the detectives had kept a good watch. It proved that the crystal stopper was still in the Square Lamartine.

It was still there; and this showed either that Daubrecq had not ventured to go home, or else that his state of health hindered him from doing so, or else again that he had sufficient confidence in the hiding-place not to trouble to put himself out.

In any case, there was no doubt as to the course to be pursued: Lupin must act and he must act smartly. He must forestall Daubrecq and get hold of the crystal stopper.

When they had crossed the Bois de Boulogne and were nearing the Square Lamartine, Lupin took leave of the doctor and stopped the car. The Growler and the Masher, to whom he had wired, met him.

"Where's Mme. Mergy?" he asked.

"She has not been back since yesterday; she sent us an express message to say that she saw Daubrecq leaving his cousins' place and getting into a cab. She knows the number of the cab and will keep us informed."

"Nothing further?"