"But enough of that. Now, I have a trifling favor to ask of you--something concerning the laboratory. Will you please return to it." A strange light glimmered for an instant in Dr. Ku Sui's eyes--a mocking of the slender man before him. Only for an instant; then it was gone. Gracefully he raised his tall figure. "The laboratory? Of course, my friend. And as for the favor--almost anything." CHAPTER VI _The Deadline_ Friday greeted them with another wide grin, and would again have bludgeoned the Eurasian with his wit had not the Hawk motioned him to silence. Looking at Dr. Ku, he said: "I have Friday posted here because of the secret panel somewhere in this wall. You escaped through it before--do you remember?" "Of course I remember. And if I'd had merely a fraction of your luck then, my present situation would be quite different." "Perhaps," said the Hawk. "This panel is now the unknown quantity so far as I'm concerned, and I don't like unknown quantities; so I am asking you to show me where it is and how it works. That's my favor. Of course you can refuse to reveal it, but that will not delay me very long. The method of compulsion I mentioned...." Dr. Ku-Sui appeared to reflect a moment, but his decision was not tardy in coming. He smiled. "You terrify me, Captain, with your ominous hints about compulsion. I suppose I'd better be reasonable and show it to you. Really, though, your concern over the panel is rather wasted, inasmuch as it conceals nothing more than a small escape passage leading out of this building. Nothing important at all." But his words, Carse somehow felt, were a screen; something else lay beneath them. He watched the tall figure with its always present odor of tsin-tsin blossoms move forward in a few indecisive steps, then back again, considering. The smile and the easy words were a camouflage, surely--but for what? "Nothing important at all." Dr. Ku Sui repeated pleasantly. "Come. I will show you. Friday--if I may so address you--over on that switchboard you will find a small lever-control. It is the one with a Chinese character above it. Will you be so kind as to throw it?" The Negro glanced inquiringly at his master. Grimly Carse nodded. An enigmatic light glimmered in the Eurasian's green eyes as they watched the Negro go to the switchboard and put thumb and forefinger on the control. "Only a small escape passage," he said deprecatingly as the Hawk crouched, gun ready, his eyes on the suspected place in the wall. Friday threw the switch. Immediately there sounded a short, sharp explosion. And acrid smoke billowed out from under the case of coordinated brains! * * * * * Carse sprang to Ku Sui, gripped one arm and cried harshly: "What have you done?" "Not I, Captain--your obedient servant, the Black. Please, your fingers--" He removed them from his arm; and then, smiling, he said: