Then while John and Tom went industriously to work, Paul and Bob rode away to Clark Polytechnic in New York with Mr. Giddings. Just before starting into the city that morning, the newspaper man had met Tom, and there was little doubt that he was well pleased with this addition to his force of workers. Of course Paul and Bob were sorry to have to interrupt their labors on Sky-Bird II, but there was no help for it, and there was some consolation in the thought that undoubtedly their instructors would let them work on some of the airplane's smaller parts as a portion of their school mechanical practice. This supposition indeed proved correct, and as the fall days passed they found the two student chums not only partaking with full spirit in the sports of their comrades, but also contributing in no small measure to the progress of the work on the new airplane. As a rule, Paul and Bob managed to stop in each Saturday for at least an hour or so to lend some assistance to John and Tom, and when there were no school contests on, they spent practically the entire holiday in the hangar. The cool days of November soon compelled the boys to install a couple of heating stoves in the big building, and after that the place was warm and cheery throughout the working day, no matter how blustery and nippy the weather. At night the coals were carefully banked with ashes, to keep up a fair degree of warmth until the following morning. Up to this time nothing had been seen of any suspicious person lurking around the premises, but one afternoon late in the month, when Tom Meeks was working alone in the hangar and John had gone to town after some bolts, Tom thought he heard a strange sound at one of the two windows near the workbench. Turning quickly from the wing-strut which he had been setting in place, Tom faced the window just in time to see a swarthy-looking countenance, adorned with a toothbrush-like mustache, pulled out of range. The mechanic had been informed of Bob's experience with the man who had evidently followed him to the grounds during the summer, also of the blue-prints which had been stolen, and now as he observed the similarity in looks between this eavesdropper and the reported shadow of Bob, he became quite excited. With that lack of coolness and presence of mind characterizing a more reserved temperament, the impulsive Tom rushed straight up to the window, and peered out. Of course he could see nothing, for the peeper had been cute enough upon finding himself observed to keep close to the side of the building as he moved swiftly toward its rear. Tom now seized the lower sash and tried to throw it up, so as to get a sidewise view. To his disgust he found it double-spiked, and realized that he had put that very second nail in himself upon first learning of the loss of the blue-prints. "Huckleberry pie!" sputtered Tom, using his favorite expression when excited.