For all their experience with the desert, they had never happened to hear just that thing.

The Arab, however, felt a stab of profound anxiety.

His lips moved in a silent prayer to Allah.
Once more the Master raised his hand in signal of advance.

The three man-stalkers wormed forward again.

They now had their direction, also their distance, with extreme precision; a simple process of triangulation, in which the glow of the beach-fire had its share, gave them the necessary data.
Undaunted, they approached the camp of the Beni Harb; though every moment they expected to be challenged, to hear the crack of an alarm-rifle or a cry to Allah, followed by a deadly blast of slugs.
But fortune's scale-pan dipped in their direction, and all held still.
The sun-baked desert kept their secret.