Once again that hollow moaning sound drifted in across the baked expanse of the Sahara—­a strange, empty sound, unreal and ominous.  Then came a stir of sultry breeze, from the east.  It strengthened; and a fine, crepitant sliding of sand-particles became audible.  Rrisa stirred uneasily.

“Master,” he whispered, “we should not delay.  If the jinnee of the waste overtake us, we may be lost.”

“The jinnee of the waste?” the Master answered, in a low tone.  “What nonsense is this?”

“The simoom, Master—­the storm of sand.  We call it the work of evil spirits!”

The Master made no reply, save to command silence.

For a time nothing happened in the Arabs’ camp.  Then came a little stir, off there in the gloom.  A sound of voices grew audible.  The name of Allah drifted out of the all-enveloping night, to them, and that of his Prophet.  A cry:  “Ya Abd el Kadir—­” calling on a patron saint, died before the last word, “Jilani,” could find utterance.  Then silence, complete and leaden, fell with uncanny suddenness.

The Master laughed, dryly.  He touched Leclair’s arm.

“Strong medicine for the Beni Harb, Lieutenant,” said he.  “Their own imams (priests) have strong medicine, too, but not so strong as that of the cursed sons of Feringistan.  Sleep already lies heavy on the eyelids of these sons of Allah.  And a deeper sleep shall soon overcome them.  Tell me, Lieutenant, can you kill men wholesale?”

“Yes, my Captain.”

“Sleeping men, who cannot resist you?  Can you kill them scientifically, in masses, without anger?”

“How do you know now, my Captain, that it will not be in anger?” And the Frenchman half eased himself up on hands and knees, peering forward into the night.  “After what these Beni Harb—­or their close kin—­have done to me and to poor Lebon—­listen!  What was that?”

“What do you mean?”

“That far, roaring noise?”

“It is nothing!  A little wind, maybe; but it is nothing, nothing!  Come, I am ready for the work!”

The Master stood up.  Rrisa followed suit.  No longer crawling, but walking erect, they advanced.  They still used caution, careful to make no noise; but confidence had entered into them.  Were not the Arabs all asleep?

The white men’s faces were pale and drawn, with grim determination for the task that lay ahead—­the task of converting the Beni Harb’s camp into a shambles.  The Arab’s face, with white-rimmed eyes and with lips drawn back from teeth, had become that of a wild animal.  Rrisa’s nostrils were dilated, to scent out the enemy.  He was breathing hard, as if he had run a mile.

“They are near, now, Ya M’alme!” said he.  “They are close at hand, these nakhawilah! (pariahs).  Allah, the high, the great, hath delivered them into our hands.  Verily there is no power or might but Allah.  Shall I scout ahead, Master, and spy out the camp?”