“We must,” exclaimed Roy, with a serious note in his voice; “if this wind freshens much more we won’t be able to turn at all.”

He leaned forward and took the wheel from his sister. But the instant he tried to steer the aeroplane round, the wind, rising under one wing tip, careened her to a perilous angle.

“No go,” he said; “we’ve got to keep on going.”

“But where can we land?” asked Peggy, a little catch in her voice.

“We’ll have to take chances on that,” decided Roy. “It would be suicidal to try to buck this wind.”

The breeze had now freshened till it was singing an Aeolian song in every wire and brace of the Golden Butterfly. Brother and sister could feel the stout fabric vibrate under the strain of the blast.

The aeroplane was moving swiftly now. But it was the toy of the wind, which grew stronger every minute. The dark landscape beneath fairly flew by under them. Neither of them thought to look back at the red and green lights in the sky behind them.

All at once, Roy, who had leaned over his sister’s shoulder and glanced at the compass, gave a sharp cry.

“We’ve got to turn, sis,” he said, in a tense, sharp voice.

“What do you mean, Roy? Are we in any very serious danger?”