"Let us take the one on the right," said Keane, indicating the latter. "It is more likely to yield us something," and the next moment they were hidden from sight amid the dense undergrowth of this part of the forest. Scarcely had they disappeared from view when one of the upper branches of a tree near to the edge of the clearing suddenly appeared to move, then to swing loosely for a second, and drop to the ground. Then for a moment there was silence, save for the call of a nightjar which had been disturbed, but a moment later a dark shadow debouched from the edge of the forest and crossed quietly but quickly to where the fire had been burning a few minutes previously. A low whistle, repeated twice, brought a similar shadow from the opposite side of the clearing, and the two indistinct, but human shapes, met each other face to face. "Who were they, Professor?" asked the second arrival of the first. "Himmel! Ich weiss nicht, Strauss," replied his companion, who was none other than the renowned Professor Rudolf Weissmann, "but I fear that they portend us no good." "Let us examine the ground to see if they have left any clue behind." So for the next few minutes the professor and his mechanic searched the ground carefully for any little souvenir which the travellers might have left behind them. And whilst they searched, they talked in low, but eager whispers. "Did you hear that half-witted Schwarzwalder talking aloud about the _Scorpion_?" asked the professor. "Yes. He called it a phantom-bird, did he not?" replied Strauss. "I heard nearly all he said, he spoke so loudly and coarsely." "Could you hear what the others said?" "Not a word; they spoke so quietly, save once or twice when they spoke to the clock-maker." "Nor could I, and that is what makes me so suspicious," returned Weissmann. "They spoke good German, though," ventured the mechanic. "Bah! Of course they would. Nevertheless, it’s my firm opinion that they’re foreigners, and that they’re here for some special reason." "And that reason is?" "To find out about the _Scorpion_," snarled the mathematician. "Ach!" exclaimed the other; "the _Scorpion_ is two thousand miles away." "Then their next business is to find the aerodrome," said the professor. "Blitz! that they’ll never do except by accident. Think of those live wires waiting for them if they get within a hundred yards of it. We have found six dead men there already; I don’t want to dig any more graves," returned Strauss.