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.