* * * * *

The next day three of the native servants became violently ill, seized by the most appalling convulsions.  At first, a thrill of horror ran through the chateau.  The plague!  The plague in reality!  Faces blanched white with dread, hearts turned cold and sank like lead; a hundred eyes looked out to sea with the last gleam of hope in their depths.

But these fears were quickly dissipated.  Baillo and the other natives unhesitatingly announced that the men were not afflicted with the “fatal sickness.”  As if to bear out these positive assertions, the sufferers soon began to mend.  By nightfall they were fairly well recovered.  The mysterious seizure, however, was unexplained.  Chase alone divined the cause.  He brooded darkly over the prospect that suddenly had presented itself to his comprehension.  Poison!  He was sure of it!  But who the poisoner?

All previous perils and all that the future seemed to promise were forgotten in the startling discovery that came with the fall of night.  The first disclosures were succeeded by a frantic but ineffectual search throughout the grounds; the chateau was ransacked from top to bottom.

Lady Deppingham and Robert Browne were missing!  They had disappeared as if swallowed by the earth itself!

Neenah, the wife of Selim, was the last of those in the chateau to see the heirs.  When the sun was low in the west, she observed them strolling leisurely along the outer edge of the moat.  They crossed the swift torrent by the narrow bridge at the base of the cliff and stopped below the mouth of the cavern which blew its cool breath out upon the hanging garden.  Later on, she saw them climb the staunch ladder and stand in the black opening, apparently enjoying the cooling wind that came from the damp bowels of the mountain.  Her attention was called elsewhere, and that was the last glimpse she had of the two people about whom centred the struggle for untold riches.

It was not an unusual thing for the inhabitants of the chateau to climb to the mouth of the cavern.  The men had penetrated its depths for several hundred yards, lighting their way by means of electric torches, but no one among them had undertaken the needless task of exploring it to the end.  This much they knew:  the cavern stretched to endless distances, wide in spots, narrow in others, treacherous yet attractive in its ugly, grave-like solitudes.

“God, Chase, they are lost in there!” groaned Deppingham, numb with apprehension.  He was trembling like a leaf.

“There’s just one thing to do,” said Chase, “we’ve got to explore that cavern to the end.  They may have lost their bearings and strayed off into one of the lateral passages.”

“I—­I can’t bear the thought of her wandering about in that horrible place,” Deppingham cried as he started resolutely toward the ladders.

“She’ll come out of it all right,” said Chase, a sudden compassion in his eyes.