"Twenty years ago," he said, "Lynch, Hopkins and myself, young men just out of college, were in China, in the employ of the war-lord Yuen Chin. We were chemical engineers. Yuen Chin was a far-sighted man—ahead of his time, scientifically speaking. He visioned the day when men would war with gases and deadly chemicals. He supplied us with a splendid laboratory, in which to discover or invent some such element of destruction for his use.
"He paid us well; the foundations of all of our fortunes were laid there. We were young, poor, unscrupulous.
"More by chance than skill we stumbled onto a deadly secret—the formula for a poisonous gas, a thousand times more deadly than anything yet dreamed of. That was what he was paying us to invent or discover for him, but the discovery sobered us. We realized that the man who possessed the secret of that gas, could easily conquer the world. We were willing to aid Yuen Chin against his Mongolian enemies; we were not willing to elevate a yellow mandarin to world empire, to see our hellish discovery directed against the lives of our own people.
"Yet we were not willing to destroy the formula, because we foresaw a time when America, with her back to the wall, might have a desperate need for such a weapon. So we wrote out the formula in code, but left out three symbols, without any of which the formula is meaningless and undecipherable. Each of us then, had a lower jaw tooth pulled out, and on the gold tooth put in its place, was carved one of the three symbols. Thus we took precautions against our own greed, as well as against the avarice of outsiders. One of us might conceivably fall so low as to sell the secret, but it would be useless without the other two symbols.
"Yuen Chin fell and was beheaded on the great execution ground at Peking. We escaped, Lynch, Hopkins and I, not only with our lives but with most of the money which had been paid us. But the formula, scrawled on parchment, we were obliged to leave, secreted among musty archives in an ancient temple.
"Only one man knew our secret: an old Chinese tooth-puller, who aided us in the matter of the teeth. He owed his life to Richard Lynch, and when he swore the oath of eternal silence, we knew we could trust him."
"Yet you think somebody is after the secret symbols?"
"What else could it be? I cannot understand it. The old tooth-puller must have died long ago. Who could have learned of it? Torture would not have dragged the secret from him. Yet it can be for no other reason that this fellow you call Yarghouz Barolass murdered and mutilated the bodies of my former companions, and now is after me.
"Why, I love life as well as any man, but my own peril shrinks into insignificance compared to the world-wide menace contained in those little carven symbols—two of which are now, according to what you say, in the hands of some ruthless foe of the western world.
"Somebody has found the formula we left hidden in the temple, and has learned somehow of its secret. Anything can come out of China. Just now the bandit war-lord Yah Lai is threatening to overthrow the National government—who knows what devilish concoction that Chinese caldron is brewing?
"The thought of the secret of that gas in the hands of some Oriental conqueror is appalling. My God, gentlemen, I fear you do not realize the full significance of the matter!"
"I've got a faint idea," grunted Rollins. "Ever see a dagger like this?" He presented the weapon that had killed the Mongol.
"Many of them, in China," answered Willoughby promptly.
"Then it isn't a Mongol weapon?"
"No; it's distinctly Chinese; there is a conventional Manchu inscription on the hilt."
"Ummmmmm!" Rollins sat scowling, chin on fist, idly tapping the blade against his shoe, lost in meditation. Admittedly, he was all at sea, lost in a bewildering tangle. To his companions he looked like a grim figure of retribution, brooding over the fate of the wicked. In reality he was cursing his luck.
"What are you going to do now?" demanded Hoolihan.
"Only one thing to do," responded Rollins. "I'm going to try to run down Yarghouz Barolass. I'm going to start with River Street—God knows, it'll be like looking for a rat in a swamp. I want you to contrive to let one of those Mongols escape, Hoolihan. I'll try to trail him back to Yarghouz's hangout—"
The phone tingled loudly.
Rollins reached it with a long stride.
"Who speaks, please?" Over the wire came a voice with a subtle but definite accent.
"Brock Rollins," grunted the big dick.
"A friend speaks, Detective," came the bland voice. "Before we progress further, let me warn you that it will be impossible to trace this call, and would do you no good to do so."
"Well?" Rollins was bristling like a big truculent dog.
"Mr. Willoughby," the suave voice continued, "is a doomed man. He is as good as dead already. Guards and guns will not save him, when the Sons of Erlik are ready to strike. But
