"You unearthed a gold mine for the colonel, Dave!" Freddy Farmer cried excitedly. "Now British Intelligence can throw out a dragnet and catch every--No?" Young Farmer checked himself and spoke the last as Dawson made a wry face and shook his head. "No, Freddy," Dave said sadly. "Unless Herr Baron is a complete dope, which he sure isn't. You're forgetting that the rat got away from us, Freddy. He'll discover that his little book is gone, and the first thing he'll do is to make sure his agents clear out and clear out fast. Am I right, Colonel?" "I'm afraid you are, Dawson," the senior officer agreed with a heavy sigh. "He'll do just that, unquestionably. Now, if only we had captured him with this little book, then--But we can't expect everything to go in our favor. But let me continue with what is perhaps the most important item in this little black book. This will interest you particularly, Major. There are several references to Number Sixteen Kholerstrasse!" Major Crandall sat up straight, as though he had been shot. "No?" he gasped. "You mean--?" "Exactly, Major," Colonel Fraser interrupted. "Number Sixteen Kholerstrasse in the city of Duisburg, Germany. He has listed here certain dates when his agents are to report to Number Sixteen Kholerstrasse. And the last date, which he has underscored several times, is the twenty-fourth of this month!" "So the rats are all going back to the same hole!" Major Crandall said softly, as though he couldn't believe his own words. "But--but to tell the truth I've been doing a little thinking about Sixteen Kholerstrasse lately. Four of the mystery factories are located in the Duisburg area. The nerve of those rats! Using the very nest we thought we'd smoked out for keeps. Right now I don't know whether that's being clever, or being damn fools, to tell you the truth." "It was being blasted clever, until Dawson got hold of _this_!" Colonel Fraser said, and held up the little black book. "Frankly, I'd never have suspected that they would use the same place again. But that's the Hun for you. They are very likely to do the totally unexpected, ingrained as they are with routine. But they're a queer race, anyway." "And one the world could well do without!" Dawson said grimly. "But is it permitted to ask questions at this point, sir?"