The fellow continued to sway himself back and forth, peering as if his eyes were about to leave his head.  For a long moment or two he utterly disregarded O’Reilly, but finally as he gained more self-control his gaze shifted and his expression altered.  He changed his weight to his left arm and with his right hand he drew his revolver.

“What are you doing?” O’Reilly cried, hoarsely.

The colonel seemed vaguely surprised at this question.  “Fool!  Do you expect me to share it with you?” he inquired.  “Wait!  There’s enough—­for all of us,” O’Reilly feebly protested; then, as he heard the click of the cocked weapon:  “Let me out.  I’ll pay you well—­make you rich.”  In desperation he raised his shaking hand to dash out the candle, but even as he did so the colonel spoke, at the same time carefully lowering the revolver hammer.

“You are right.  What am I thinking about?  There must be no noise.  Caramba!  A pretty business that would be, wouldn’t it?  With my men running up here to see what it was all about.  No, no!  No gunshots, no disturbance of any kind.  You understand what I mean, eh?”

His face twisted into a grin as he tossed the revolver aside, then undertook to detach a stone from the crumbling curb.  “No noise!” he chuckled.  “No noise whatever.”

O’Reilly, stupefied by the sudden appearance of this monstrous creature, stunned by the certainty of a catastrophe to Rosa, awoke to the fact that this man intended to brain him where he stood.  In a panic he cast his eyes about him, thinking to take shelter in the treasure-cave, but that retreat was closed to him, for he had wedged the wooden timbers together at the first alarm.  He was like a rat in a pit, utterly at the mercy of this maniac.  And Cobo was a maniac at the moment; he had so far lost control of himself as to allow the stone to slip out of his grasp.  It fell with a thud at O’Reilly’s feet, causing the assassin to laugh once more.

“Ho, ho!” he hiccoughed.  “My fingers are clumsy, eh?  But there is no need for haste.”  He stretched out his arm again, laid hold of another missile, and strained to loosen it from its bed.  “Jewels!  Pearls the size of plums!  And I a poor man!  I can’t believe it yet.”  He could not detach the stone, so he fumbled farther along the curbing.  “Pearls, indeed!  I would send a dozen men to hell for one—­”

O’Reilly had been standing petrified, his body forced tightly against the rough surface behind him, following with strained fascination the deliberate movements of the man above him; now he saw Cobo, without the least apparent reason, twist and shudder, saw him stiffen rigidly as if seized with a sudden cramp, saw his eyes dilate and heard him heave a deep, whistling sigh.  O’Reilly could not imagine what ailed the fellow.  For an eternity, so it seemed, Cobo remained leaning upon his outspread arms, fixed in that same attitude of paralysis—­it looked almost as if he had been startled by some sound close