“If there are traitors in the army and navy, why not in the aeroplane factories, too?” suggested Fleck.  “A spy in the shipping department could easily change the label on even a Liberty motor intended for one of Uncle Sam’s flying fields.  Even when it didn’t turn up where and when it was expected, it would take government red tape three months to find out what had become of the missing motors.”

“These machines”—­said Jane suddenly, “they must be the ‘wonder-workers’ old Mr. Hoff was always talking about.”

“And that last advertisement we read,” Dean reminded them, “announced that the wonder-workers would be ready Friday.  It looks as if we got here not a minute too soon.”

“You bet we didn’t,” said Carter.  “Every one of those three planes is fairly loaded down with big bombs, scores of them.”

“To bomb New York,” said Fleck soberly; “that’s their plan.  Zeppelins for England, big guns to shell Paris, bombs from the air for New York.  It’s part of their campaign to spread frightfulness, to terrorize the world.  Undoubtedly that is the reason Berlin sent Frederic Hoff over here, to superintend the destruction of the metropolis.  There have been whispers for months and months that the city some day was to be bombed, but we never were able to discover their origin.”

“And not a single anti-aircraft gun or anything in the whole city to stop them, is there?” cried Jane.  “Wouldn’t it be terrible?”

Fleck smiled grimly.

“Any foolhardy German who tries to bomb New York from the air has a big surprise coming to him—­a lot of big surprises.  The war department may not have been doing much advertising, but it has not been idle.”

“Then we have some anti-aircraft guns!” cried Jane delightedly.  “I never heard anything about them.”

“That would be telling government secrets,” said Fleck, smiling mysteriously, “but I’d just like to see them try it.  I have sort of a notion to let them start their bombing.”

“Oh, no, we mustn’t,” Jane insisted.  “We mustn’t let those aeroplanes ever start.  Can’t we do something right away to cripple them?”

“There’s plenty of time,” the chief assured her.  “It is best for us to wait until after dark.  The early morning would be ideal time for an aerial attack on the city, when everybody is helpless and asleep.  There’s generally a fog over the river and harbor, too, before sunrise at this season of the year, and that might help them to mask their movements.  It would take an aeroplane less than an hour to reach the city from here, so that there is no likelihood of their starting until long after midnight.  That gives us plenty of time, and besides we must wait until the Hoffs arrive.”

“That will make two more—­sixteen of them against our nine,” warned Dean.

“We cannot help it how many of them there are,” said Fleck.  “It is of vital importance for us to know just what their plans are.  It is unlikely that they will post guards to-night in this secluded spot, where they have been at work in safety for months.  As soon as it is dark we can smash the aeroplanes.”