Then, untethering his pack-horse, he thanked the strangers for their hospitality, gave them the direction and situation of his cottage, where they would be welcome, should they care to visit him during their stay in the Schwarzwald, and, bidding them adieu, started off on his journey through the forest. *CHAPTER XVII* *THE WATCHERS* They watched the Schwarzwalder and his beast of burden disappear into the forest, then for some minutes the two Englishmen, buried in thought, sat by the embers of the fire. Neither spake to his companion for a while, as, deep in contemplation, each endeavoured to fathom in his own mind this secret of the phantom aeroplane, this riddle of the sphinx. At last Keane addressed his colleague. "This travelling clock-maker has confirmed our theory, Sharpe," he said. "Yes, the simple fellow has helped us not a little," replied the other. "We must continue our search without further delay, lest this talkative peasant should himself encounter this genius, and unwittingly announce the presence of two strangers in the forest. That is my great fear now." "You don’t think this fellow misled us, Keane?" "Why do you ask? He was too dull-witted to be anything in the nature of an accomplice," replied the captain. "Quite so, but he might have been a tool in the hands of this mystery man," added Sharpe, as a sudden feeling of suspicion shot across his mind. "In that case we ought to have followed him, but I scarcely think it worth while. A dull-witted man of that type would have been too dangerous to his employer, even when used merely as a tool. The only danger I anticipate from that quarter, unless I am utterly mistaken, is that the fellow may encounter someone in the forest who is engaged in the plot, and thus reveal our presence, as I stated previously," observed Keane, as he began to get his traps together, ready for the march. "Anyhow, we have learned something from the Schwarzwalder." "By the way, Sharpe, you might tune up your little wireless pocket ’phone, and ascertain if there are any messages floating around." "So I will; we might pick up something," replied the junior airman, and the next moment he climbed into a straggling, low-branched tree, uncoiled a small aerial, and, starting his little battery, listened attentively for any stray message that might be floating through the ether. "Anything?" asked Keane, coming to the foot of the tree. "Nothing," remarked the other. "Then we’ll push off." Five minutes later, having adjusted their packs, collected their nets, and having stamped out the remains of the fire, they were ready to start. "Which path shall we take?" asked Sharpe, for there were two ill-defined, grass-grown tracks which led away from the clearing. One led past Jacob Stendahl’s cottage, and had been followed by the Schwarzwalder, and the other, the lesser trodden of the two, led they knew not where.