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."
"That's so," agreed his superior thoughtfully. "You might see if the Remington people can give us any help with that. If possible, get a list of all the people who have bought machines during this last six weeks. It's a long shot, but long shots sometimes come off. And if you come into my room I'll give you a pistol. It'll be as well for you to carry one while you're on this case. I was shot at myself, to-day."
"Thank you, sir, I think I'll do without one," said the other quietly. "My two fists are good enough for me."