Her mind had reverted, as she found it frequently doing, to Frederic Hoff and the sealed packet he had entrusted to her.  He had professed to love her and had demanded that she trust him.  Was it, she wondered, all a base pretense on his part?  Was he—­for Germany’s sake—­taking advantage of her affection for him to make her the unwitting custodian of some secret too perilous for him to carry about with him?  Perhaps that little parcel she was carrying in the bosom of her gown contained the code he and his uncle used?  Had it not been for Dean’s presence she might have been tempted to take Fleck into her confidence and tell him of the peculiar incident, though in spite of all she knew about him she felt that Frederic Hoff’s feeling for her was real, and that toward her he always would show only respect and honor, as he always had done hitherto; and yet—­

Before the chief had time to answer her question Dean with a whispered “hist” pointed to a path in the rear of the buildings they were watching.  Behind the house two rugged hills, their sides of precipitous rock so steep that they hardly afforded a foothold, came down close together, making a V-shaped cleft through which a narrow path ran in the direction of the river.  Looking toward this cleft to which Dean was pointing they now saw a group of workmen approaching the house.

All of them were in the garb of mechanics, yet as they approached in single file down the path, the quick eye of the chief noted that they were keeping step.

“They’ve all of them seen service,” he muttered to himself, “either in prison or in the German army.”

Some of them carried kits of tools, and they walked with the air of fatigue that results from a day of hard physical work.  They seemed to have no suspicion as yet that they were under observation, for as they walked they chatted among themselves, the sound of their German gutturals reaching the watchers, but unfortunately not distinctly enough to be audible.  Dean was busy counting them.

“There are fourteen,” he announced, “two more than we were expecting to find here.”

“At what do you suppose they are working?” asked Jane curiously.

“Here comes Carter,” replied Fleck.  “Perhaps he can tell us.  His face shows that he has learned something.”

Carter, crawling rapidly but silently through the underbrush, approached breathlessly, his sweaty, begrimed countenance ablaze with excitement.

“What’s up?” asked Fleck, as soon as he was within hearing.

“My God, Chief,” he gasped, “they’ve got three big aeroplanes out there on a plateau overlooking the river—­three of them all keyed up and ready to start.”

“Friends of the Air,” muttered Fleck; “so that’s what it means.”

“They’ve evidently smuggled all the material up and built the three planes right here,” Carter went on.  “I watched them putting on the finishing touches and testing the guy-wires.  There is a machine shop, too, rigged up in one of those outbuildings.  The thing that gets me is how they got the engines here.  All the planes are equipped with powerful new engines.”