It was not the machine manned by Secret Service Agent Ford and his companion, but a much heavier and more rapid vehicle. And until its shadow fell across the Snowbird, the boys had had no warning of its approach.
At first glance it was apparent that the strange aircraft intended mischief. It was shooting down from a higher level, its sharp bow aimed directly for the Snowbird. Jack pushed over the switch and raised the bow of their own ship. She leaped forward and began to slant upward, too.
But instantly the course of the stranger was deflected to meet this change in the movement of the Snowbird. She had the advantage of the boys' craft, too. She evidently proposed to retain her overhead position, and as she shot in closer, Jack was constrained to descend again to escape collision with her.
"Keep away!" he shouted through the transmitter, and at his cry, and the bustle about him, the professor was awakened.
But no reply came from the strange aeroplane, although they could see several figures moving upon her. It swooped down upon them, and Jack had to deflect his planes again and slant downward toward the storm-cloud.
And then he saw the other peril. He was between two great dangers. If the reckless aviator tried to ram him from above, his only escape was by plunging through the tempest which raged just below them.
Down came the stranger upon the Snowbird again. She surely meant them ill—she was bent on their destruction. And meanwhile the thunder roared below and the crackling of the lightning was almost incessant.
Jack Darrow had to decide quickly—and he must determine which of the two risks to take.