A few moments later Burnet also detected another sound mingling with the drone--the unmistakable thud of hoofs. The explanation flashed upon him. The troopers who had ridden from the scene of the previous day's incident had been despatched to the Turkish outpost of which Rejeb had told him, and were now returning, accompanied by a motor launch on the wady, no doubt sent to transport the aeroplane by water. He imparted his conclusion to Rejeb. "Wallahi!" exclaimed the chief. "An evil spirit is striving against us." One thought had flashed upon the young men at the same moment. They might rout the Turks, but lose the aeroplane. The enemy would no doubt place on the deck of the launch not only the machine, but their prisoner, and the Arabs could not fire on the crew without the risk of hitting the Englishman. It was possible, of course, to hold up the launch and prevent it from passing up the wady, but the sound of rifle shots could not fail to be heard by the Turks conveying the aeroplane, and the alarm would ruin the chances of a successful ambuscade. While Rejeb and Burnet were discussing the matter in low tones, they peered out through the reeds in the direction of the rapidly approaching sounds. Soon they caught sight of six horsemen riding in couples along the bank of the wady, and as they drew abreast, the launch became visible beneath their horses' bellies. One of the horsemen was an officer, whom no doubt the news brought him at the outpost had induced to ride back with the messengers and see for himself the captured aeroplane. Launch and horsemen passed out of sight. During the few moments' pause in the conversation while the enemy went by, an idea had occurred to Burnet. It was probable that the aeroplane had barely arrived at the bank of the wady, and, judging by the direction of its captors' march, at a point at least five or six miles from the ruins. The launch was keeping pace with the horsemen on the bank; it might reach the aeroplane in something under an hour. Further time would be occupied in explanation; no doubt the officer from the outpost would be curious enough to examine the machine; then its safe bestowal on the deck of the launch would be a long job. Probably two or three hours would elapse before the return journey commenced, and Burnet had conceived a plan for utilising those hours.