The Radio Boys with the Revenue Guards

Bob swooped so low the plane almost skimmed the water, and all three obtained a good view of the stranger, before once more Bob soared aloft and forged ahead. Looking back, Frank trained the glasses on the scene. But nobody appeared from among the trees, and, far as they could determine, they were unobserved. They made a quick run to their own landing field, descended and put the plane away. Not until the doors were closed and locked did they sit down on the skidway outside the hangar to discuss what they had seen. There had been remarks made by all after they had seen the strange plane at close range and on the hasty trip home, but all had been too busy with their own thoughts for extended discussion. Discovery of the plane had altered their original plans to fly over the secret radio station. They had decided not to advertise their presence as, if Frank was correct in his surmise that the other plane had been watching.