"If this mysterious disease isn't checked it will be worse than the 'flu,'" said Bart. "What's the matter with our doctors anyway? Why don't they get on the job?" "You can't blame them," Frank defended. "There's no better medical staff in any army than the one we've got. They're working like mad to try to isolate the germ, or whatever it is, that's causing this mysterious trouble. But they seem to be all at sea in this matter. It's an entirely new thing, and they haven't found any way to conquer it." "It would be rather hard luck to come through St. Mihiel and the Argonne, and then to be knocked out by a measly disease like this," said Billy disgustedly. "Well, it hasn't got us yet, and let's hope it won't," said Frank. "But now that we've got a chance, what do you fellows say if we go over tonight and try to get at the bottom of that alley mystery? I shan't be easy in my mind until I've solved it." "Always looking for trouble," laughed Bart. "But I don't mind confessing that the matter's got tight hold of me too, and I'm game to see it through to a finish." "Count me in," said Billy. "If only poor Tom were with us!" mourned Frank "It's just the kind of thing he'd like to trail. And if there should happen to be any scrapping, he'd be a mighty handy lad to have along with us. He'd rather fight than eat any time." After the drills and work of the day were over they got permission to go to the town and started across the river just as twilight was falling. While passing through one of the streets, they met the famous German physician, from whom they customarily got a look that betrayed his hate of the American uniform. But this time, to their surprise, he was rubbing his hands and seemed to be in high good humor. "What's come over his nibs, I wonder," remarked Billy. "Usually he seems to have a grouch of the worst kind, but to look at him now you might think that he'd just had news of a good fat legacy." "He is different, for a fact." agreed Bart. "He couldn't look happier if Germany had won the war." They looked after him, and saw him vanishing into the doorway of a dwelling that was really a mansion. "Swell place that," observed Billy. "He must have a peach of a practice to live in a house like that." "He's one of the most famous men in his line in Germany I've heard," commented Frank. "They say the Kaiser himself used to consult him. But of late they say that he's made himself almost a hermit. Seems that he's given up his regular practice, and simply nurses his grouch because Germany was licked." "He sits up pretty late to do it then," put in Billy. "I've been on sentry duty in this street, and many a time I've seen a light in his office until almost morning." "Here's our corner," Frank said, as they came to the next street. They approached the alley with the utmost caution, and slipped into its darkness when they felt sure that they were unobserved.