A faint humming sound came from the distance, gradually growing louder.
The aëroplane was returning.
Even as this conviction darted into his mind, the vast shape flashed by high in the air. For a second the shadowy form was barely discernible against the glittering stars, and then it vanished from sight among the mountains.
“Back again, eh?” commented the Texan. “What do you know about that? I tell you, pard, this here gent has sure got me guessing some.”
Starting the engine with a flip of the crank, Dick took his seat at the wheel and Buckhart climbed in beside him.
“You’re not the only one he has guessing,” Merriwell remarked, after he had turned the car and started back. “He’s a most perplexing mystery, and I rather think we couldn’t spend to-morrow more profitably than in trying to solve that problem.”
For several hours that night Dick tossed restlessly on the bed. His mind was working so actively that it seemed impossible to go to sleep. Theory after theory flashed into his brain, as he sought to account for the curious behavior of Scott Randolph, only to be rejected because of some serious flaw in his reasoning. Each of the important, vital facts he had gathered concerning this mysterious man were utterly at variance with the other.
The astounding statement that he had discovered a method of manufacturing diamonds seemed to be corroborated by the drawer full of the precious gems, and also by the scrap of conversation the two Yale men had overheard in the dining room of the Brown Palace. Besides, Dick knew that diamonds had been produced by scientists, though not on a scale which made the process a scientific success. But the thing was possible.
In the face of all this stood the lie Randolph had told and the presence of the aëroplane. Why had the man kept such absolute silence about the flying machine when he had been so communicative in a far more vital matter? And more than that, why had he told Dick a deliberate falsehood in the matter of the provisions? What had been his object? What had he gained?
At last the Yale man gave it up and fell into a troubled slumber.