"That I swear it shall!"

"You're right; let's swear. Let us swear that this dead pair shall be avenged. Let us swear not to lay down our arms until the murderers of Hippolyte Fauville and his son are punished as they deserve."

"I swear it as I hope to be saved, Chief."

"Good!" said Perenna. "And now to work. You go and telephone at once to the police office. I am sure that M. Desmalions will approve of your informing him without delay. He takes an immense interest in the case."

"And if the servants come? If Mme. Fauville--?"

"No one will come till we open the doors; and we shan't open them except to the Prefect of Police. It will be for him, afterward, to tell Mme.

Fauville that she is a widow and that she has no son. Go! Hurry!"

"One moment, Chief; we are forgetting something that will help us enormously."

"What's that?"

"The little drab-cloth diary in the safe, in which M. Fauville describes the plot against him."

"Why, of course!" said Perenna. "You're right ... especially as he omitted to mix up the letters of the lock last night, and the key is on the bunch which he left lying on the table."

They ran down the stairs.

"Leave this to me," said Mazeroux. "It's more regular that you shouldn't touch the safe."

He took the bunch, moved the gla.s.s case, and inserted the key with a feverish emotion which Don Luis felt even more acutely than he did. They were at last about to know the details of the mysterious story. The dead man himself would betray the secret of his murderers.

"Lord, what a time you take!" growled Don Luis.

Mazeroux plunged both hands into the crowd of papers that enc.u.mbered the iron shelf.

"Well, Mazeroux, hand it over."

"What?"

"The diary."

"I can't Chief."

"What's that?"

"It's gone."

Don Luis stifled an oath. The drab-cloth diary, which the engineer had placed in the safe before their eyes, had disappeared.

Mazeroux shook his head.

"Dash it all! So they knew about that diary!"

"Of course they did; and they knew plenty of other things besides.

We've not seen the end of it with those fellows. There's no time to lose. Ring up!"

Mazeroux did so and soon received the answer that M. Desmalions was coming to the telephone. He waited.

In a few minutes Perenna, who had been walking up and down, examining different objects in the room, came and sat down beside Mazeroux. He seemed thoughtful. He reflected for some time. But then, his eyes falling on the fruit dish, he muttered:

"Hullo! There are only three apples instead of four. Then he ate the fourth."

"Yes," said Mazeroux, "he must have eaten it."

"That's funny," replied Perenna, "for he didn't think them ripe."

He was silent once more, sat leaning his elbows on the table, visibly preoccupied; then, raising his head, he let fall these words:

"The murder was committed before we entered the room, at half-past twelve exactly."

"How do you know, Chief?"

"M. Fauville's murderer or murderers, in touching the things on the table, knocked down the watch which M. Fauville had placed there.

They put it back; but the fall had stopped it. And it stopped at half-past twelve."

"Then, Chief, when we settled ourselves here, at two in the morning, it was a corpse that was lying beside us and another over our heads?"

"Yes."

"But how did those devils get in?"

"Through this door, which opens on the garden, and through the gate that opens on the Boulevard Suchet."

"Then they had keys to the locks and bolts?"

"False keys, yes."

"But the policemen watching the house outside?"

"They are still watching it, as that sort watch a house, walking from point to point without thinking that people can slip into a garden while they have their backs turned. That's what took place in coming and going."

Sergeant Mazeroux seemed flabbergasted. The criminals' daring, their skill, the precision of their acts bewildered him.

"They're deuced clever," he said.

"Deuced clever, Mazeroux, as you say; and I foresee a tremendous battle.

By Jupiter, with what a vim they set to work!"

The telephone bell rang. Don Luis left Mazeroux to his conversation with the Prefect, and, taking the bunch of keys, easily unfastened the lock and the bolt of the door and went out into the garden, in the hope of there finding some trace that should facilitate his quest.

As on the day before, he saw, through the ivy, two policemen walking between one lamp-post and the next. They did not see him. Moreover, anything that might happen inside the house appeared to be to them a matter of total indifference.

"That's my great mistake," said Perenna to himself. "It doesn't do to entrust a job to people who do not suspect its importance."