"Yes, the same crackling of twigs; another wild boar," remarked his friend facetiously.
Keane shook his head, for his sensitive ears had told him that the footsteps which he had heard were those of human beings. Nor was he mistaken, for a moment later they both heard distinctly, not merely the crackling of twigs and the rustle of the bracken under heavy footfalls, but voices, human voices, conversing in a guarded and careful manner.
"None of your Schwarzwald peasants this time," he murmured, fingering his Webley already, for he instinctively felt that this time they were beset by danger both before and behind. And indeed, these two men, during all their adventures in the secret service during the war, were never in more deadly peril than at this moment, as they were soon to learn.
Scarcely daring to breathe, much less to whisper now, the two Englishmen watched furtively for the coming of the strangers, who were now less than a score of yards away, but were approaching very stealthily, as though they were searching for something on the ground.
"Who can they be?" wondered Keane. "And what can they be searching for?"
"Poachers," Sharpe was thinking, "merely poachers, searching for their booby-traps."
Nearer and nearer came the dark shadows, and both the airmen had their Webleys trained on them now. In that moment they might have shot them down easily, and before long they would regret they had not done so. But that is not the English way, for the ordinary Englishman would give even a dog his chance, as the saying goes. Still, there are dogs and dogs, and sometimes human dogs are worse than the four-footed ones. But the Englishmen were uncertain; they did not know what world-wide conspirators were these two men. They did not know what fearful deeds would happen even that day on the Hamadian desert, two thousand miles away, but all of it engineered from this spot, and made possible by these two men. And as they did not know, they did not fire, but waited.
"Gott in Himmel, where does that verdammt live wire begin?" asked one of the men in a low but vehement voice. It was the professor himself, searching for one of his own man-traps.
Sharpe glanced at Keane, but the other motioned him not to fire.
"We're learning something, old man!" he whispered. "This is the gateway to the aerodrome."