"He's missing," repeated the other doggedly. "Ivan went into a shop with an entrance in two streets, and the man who was assisting Waverley slipped round to the other side. He waited there an hour, and then went to look for Waverley." The superintendent gave a short, contemptuous laugh. "Green, I guess you've been working too hard lately. You ought to apply for a fortnight's leave. Can't you see, Ivan came out and that Waverley never had time to give the tip to his man, but followed him straight away? There ought to have been three men on the job." Green drew himself up stiffly. Foyle had not recovered from the irritation caused by his own mistake, otherwise he would not have spoken as he did. Green was not the kind of man to hastily jump to conclusions. "A third was not available when Waverley left," he said. "Here is why I say Waverley is missing. It came by messenger five minutes ago, addressed to you. As senior officer I opened it." Foyle took a typewritten sheet of paper from the other's hand. It read simply-- "DEAR MR. FOYLE,--You had better call your men off. We have got one of them safe, and hold him as a hostage for our own safety. If your people go on trying to make things unpleasant for us, things will get unpleasant for him. This is not melodrama, but brutal fact." There was no signature. Foyle's square jaw became set and grim. He had no doubt that the unknown writer fully meant the threat. He liked Waverley, yet the thought of the other's peril did not sway him for a moment. The man had fallen a victim to one of the risks of his profession. "Do they expect us to back down?" asked the superintendent harshly. "If Waverley has been fool enough to get himself in a fix, he must take his chance if we can't get him out. Let's have a look at this paper." He thrust his hand in a drawer, and, flinging a pinch of black powder on the letter, sifted it gingerly to and fro. In a few seconds four finger-prints stared out blackly from the white surface. They were at right angles to the type, and just beneath it. Foyle's face relaxed in a pleased smile. "They've given us something that may help us, after all, Green," he cried. "Look here; these two middle ones are the prints on the dagger. Now let's see if we can learn anything from the typing." Half an hour later three men stood in a tiny room, darkened, save for a vivid patch of white on a screen a yard and a half square. Foyle and Green watched the screen intently as the third man inserted the slide in the powerful magic lantern. Magnified enormously, the typewritten characters stood out vividly black against the white. "What do you make of it, Green?" asked the superintendent after a pause. "Remington machine, latest pattern," answered the other briefly. "The letter 'b' slightly battered, and the 'o' out of alignment. Used by a beginner. There is double spacing between some of the lines and single in others. A capital 'W' has been superimposed on a small one."