"The price of his complicity?" he exclaimed, laying his hand upon Sturgis's arm, and looking earnestly into his eyes. "Yes," replied the reporter, steadily meeting his friend's gaze, "his daughter's hand." Sprague looked away from the honest eyes of the reporter, as if he dreaded to read in them the answer to his next question. "Who is this fiend incarnate, who is willing to traffic in his own flesh and blood, and with whom murder is a science?" "The man who is capable of these crimes, and of any others which might serve to remove an obstacle from his way, is----" The reporter did not finish his sentence. He suddenly grasped his companion by the arm and stood transfixed, his eyes dilated, his neck craned in a listening attitude, every muscle tense like those of a wild animal in ambush, about to spring upon its approaching prey. Presently a click was heard as though a bolt had been shot from its socket. "Draw your revolver!" Sturgis whispered hoarsely to his companion. "Quick!----Look there!" At the same time he drew his own weapon and pointed in the direction of the door at the head of the stairs. The door opened, and a man entered, quietly smoking a cigar. "Doctor Murdock!" exclaimed Sprague with horror. Murdock, still holding the door ajar, eyed the two men for an instant, his impassive face betraying not the slightest sign of emotion; Then, taking his cigar from his lips: "Ah, gentlemen," he drawled in his ironical way, "I am delighted to see you. I trust you will make yourselves perfectly at home for a few minutes. I shall return directly. You can continue to work out your little problem in the meantime, Mr. Sturgis." With these words he calmly turned to leave the room. "Stop!" shouted Sturgis, levelling his revolver at Murdock's head; "stand where you are or I fire!" The reporter's shot rang out almost before he had finished his sentence; but Murdock, unscathed, passed out of the room, closing the door behind him. Sprague, dazed by the rapidity with which this scene had been acted, stood rooted to the spot, without having made any attempt to use the revolver which he had drawn at Sturgis's bidding. The reporter sprang up the stairs and threw his weight against the door. But it was doubtless intended to withstand great shocks, for it remained unshaken. "Check!" came the sound of a mocking voice from the other side of the door. Then, rushing down the stairs again, Sturgis shouted to his companion: "Come quick! We must get out of here!" And he led the way through the subterranean passage toward the cellar of the Manhattan Chemical Company. CHAPTER XXI. THE DEATH CHAMBER. Before the men had gone many steps a grating sound reached their ears from the direction of the skylight. They looked up and saw sliding steel shutters slowly and ponderously close, like grim jaws; and suddenly they felt themselves cut off from the outside world.