After they had left Frank found himself very lonely, especially as he had an afternoon off duty. Mingled with his thoughts of the missing Tom was the thought that had constantly haunted his mind of late--the unsolved mystery of the alley up which hostile Germans could flit and apparently disappear into thin air. He knew there must be some explanation of the mystery, but what was it? He racked his brains to find a plausible solution. But the more he thought about it, the more uncertain he became, until at last he came to a resolution. "Here I am," he thought, "racking my wits over this matter, and about all I do is just guess work, after all. The best thing I can do is get permission to go to the town, find that alley and see if I can't run across some clue that was lacking the last time I was there." Having reached this resolve, he lost no time in acting on it, and readily securing the desired permission, he set off for the town. This he soon reached, and walked at a smart pace through the quaint, well-kept streets. Going along one broad avenue he came suddenly face to face with the man from whom he had taken away the cane, whom he had since learned was a famous German physician, a well known character throughout the war. The latter, however, was so preoccupied that he took no notice of Frank. His thoughts, whatever they were, appeared to be pleasant, for as he walked he smiled to himself and softly rubbed his hands together, as one well pleased with the course of events. "The old codger seems mightily pleased over something," mused Frank, "and I'm willing to bet a reasonable amount it isn't over any schemes for the betterment of mankind. I may do him an injustice, but I don't think his genial Hun nature is inclined exactly in that direction." He gave little further thought to the chance meeting, his mind being busied with speculations as to what he might find in the mysterious alley. The weather was very mild, and he knew the sheet of ice and snow that had covered the ground on his previous visit would not now exist to baffle him. But he did not want to enter the alley until darkness had fallen to offer him concealment, so abated his usual brisk pace to a mere saunter, and took careful note of the attitude of the people he passed. The streets were quiet enough, but the faces of the inhabitants were sullen and hostile, and Frank could read enmity in the glances cast at him. "They love the Americans about as much as they love sunstroke," he meditated. "But it doesn't matter much what they like, because they'll take just what's handed to them. But it's the lower elements and the revolutionists who are making most of the trouble, and I'm a lot mistaken if their headquarters aren't in the neighborhood of that blind alley. Well, anyway, I'll know more about it when I get through my privately conducted explorations this evening."