Meantime the spy had pulled open a drawer, from which he took a slender instrument, which also Willie could not identify. But evidently it had a sharp point; for the spy, after placing the disc on the dollar, scratched the milled edge of the coin with the little instrument, then he began to make marks here and there through the little disc, on the surface of the dollar. From time to time he turned the coin, and occasionally he looked at the writing on his paper. He seemed quite expert, for he worked fast. He finished his task and leaned over behind his desk, evidently to put the curious disc in its secret repository.
Quick as a flash, Willie slid from his exposed perch and safely gained the concealing shelter of the lower tree tops before the spy straightened up again. Willie climbed on down the tree and joined Roy at the usual observation post.
"What did you see?" asked Roy eagerly.
When Willie had told him, Roy groaned. "Gee! That makes it all the harder. Now we've got to get one of those discs as well as a marked dollar before we can discover how they send their messages."
The grocer's boy came and went. Roy trailed him back to the store, but prudently kept out of sight. There was nothing to be gained by entering the store again. Meantime Willie scrambled up to the house and related to Lew and his captain what he had seen. And they agreed with Roy that the problem, instead of being easier, had become more difficult.
CHAPTER XIII
WHAT HENRY DISCOVERED
Henry, meantime, was waiting at his station with eagerness and quickened determination. Despite his leader's generous words, Henry felt in his heart that his last effort had been a failure. It was true that he had made it possible to learn the identity of the driver of the roadster, and that the secret service men had in the meanwhile been looking up the man's record; but Henry felt that he should also have discovered the location of the secret wireless. Now he made up his mind that nothing should balk him in the present attempt. That neither accident nor anything else should hinder him from accomplishing his purpose. He would be more skilful than he had ever been before. He would watch closer. He would follow his quarry, as silently as a shadow and as closely. He would do all that his leader expected of him—and more.
Thus resolving, steeling his mind to the greatest effort of his life, Henry stood at the little window in the garage, all atremble with eagerness. He thought he knew every inch of the spy's roadster, but when that car finally rolled past, Henry studied it as he had never studied anything before. Again he noted the tread of each tire and looked for cuts or other distinguishing marks in them. As good luck would have it, a turning wagon obstructed the roadster just as it reached the little garage, and the roadster came almost to a dead stop. Henry studied its running-gear, its radiator and bonnet, its dash-board and wind-shield. And when his eyes got so far, they went no further. The standards that held up the wind-shield were bulkier and thicker than any other such parts Henry could remember. The difference was not great, yet there was a difference; and like the accomplished scout he was, Henry noted that difference and questioned it. But, like Willie with the spider-web disc, he was completely puzzled. The enlarged standards might mean anything or nothing. The car rolled on and again Henry looked in vain at the number. Some part of it was always dust covered. But Henry observed that the hidden figures were not the same from day to day.