Down the cellar steps Brent made his way, and across the cellar floor, pausing at the rocky wall of the foundation of the house blasted and hewn out of the cliff on which it towered above the river.  A heavy steel door in the rock wall barred the way.

Brent whirled the combination and shot the bolts, and the door swung ponderously open, disclosing a rock-hewn cavern.  Three walls of the cavern were lined with shelves containing inventions of all kinds—­telegraph and telephone instruments, engine models, railroad-signaling and safety devices, racks of bottles containing dangerous chemicals and their antidotes—­all conceivable manner of mechanical and scientific paraphernalia.  It was literally a Graveyard of Genius—­harboring the ghosts of a thousand inventors’ dead hopes.

Brent entered hastily and went directly to a shelf.  There he picked up a model of a motor.  He blew the dust from it and examined it approvingly.

Suddenly he saw something that caused him to start.  He looked down at his feet.  There was a piece of paper on the floor.

He picked it up and read it, and as he did so he started back, frightened—­then angry.  He looked about at the rock-hewn cavern walls—­then read again: 

Brent—­This is my last warning.  If you persist in your course you
will be struck down by the Madagascar madness. 
Q.

Under his breath, Brent swore.  Again he looked about the cavern, then turned hurriedly, picked up the motor, passed out the steel door, clanged it shut, and locked it.

No sooner had Brent shut the door, however, than it seemed as if the very face of the outer rocky wall of the cavern began to move—­to tilt, as if on hinges.

If a human eye had been in the Graveyard of Genius at that instant it would have sworn that it perceived in the inky blackness of the tilting rock a passage, and in the shadows of that passage a huge, weird, grotesque figure peering in.

Then the tilting rock door closed again, as the figure disappeared down the rocky passage on the opposite side—­a menace and a threat to the owner of Brent Rock, insecure even in his millions.

CHAPTER II

When Brent arrived back at the library he had quite recovered his poise, at least to the eyes of those in the library.  Zita had joined Eva with the old inventor, Davis.

As Brent entered, Davis uttered an exclamation of joy at the sight of his motor.  For the moment Brent almost glowed.

“Along with your invention,” he beamed, as he handed the model to the old man, “I am going to release many others to the world.”

All this not only Locke was noting, but Zita, too, appeared to be an almost too interested listener.

The others were chatting when Zita heard a noise in the hall and hurried out.  She was just in time to see a rather hard-visaged man, with cruel, penetrating eyes.  It was Herbert Balcom, vice-president of the company.