A rifle—­probably discharged by Beatrice in a hunt after big game.  It was true that their meat supply was low; he remembered now.  Yet it was curious that she should be hunting after dark.  The gloom was deep at the cavern mouth.  Besides, he had always kept his rifle from her, fearing that she might turn it against him.  He looked about him, trying to locate the source of the flood of light on the cavern floor.  It was the moon, and it showed that the girl was gone.  He started to sit up.

But his left arm did not react just properly to the command of his brain.  It impeded him, and its old strength was impaired.  For a moment more he lay quiet, deep in thought.  Of course—­he had been injured by the falling tree.  He remembered clearly, now.  And the rifle had been broken.

The only possible explanation for the shot was that a rifle had been fired by some invader in their valley—­in all probability Neilson or one of his men.  Beatrice’s absence would also indicate this fact:  perhaps she had already joined her father and was on her way back to Snowy Gulch with him.  In that case, why had he himself been spared?

He looked out of the door of the cavern, trying to get some idea of the lateness of the hour.  The very quality of the darkness indicated that the night was far advanced.  Neilson would not be hunting game at this hour.  Was his own war—­planned long ago—­even now being waged in ways beyond his ken?

His old concern for Beatrice swept through him.  With considerable difficulty he got to his feet, then holding on to the wail, guided himself to the shelf where they ordinarily kept their little store of matches.  He scratched one of them against the wall.

In the flaring light his eyes made a swift but careful appraisal of his surroundings.  The girl’s cot had not been slept in; and to his great amazement he saw that their food supplies were spent.  Still holding to the wall he walked to the cave mouth.

Instantly his keen eyes saw the far-off gleam of the camp fire on the distant margin of the lake.  For all that the hour was late, it burned high and bright.  He watched it, vaguely conscious of the insidious advance of a ghastly fear.  Beatrice was his ally now—­if these weeks had sent home one fact to him it was this—­and her absence might easily indicate that she was helpless in the enemy’s hands.  The thing suggested ugly possibilities.  Yet he could not aid her.  He could scarcely walk; even the knife that he wore at his belt was missing, probably carried by Beatrice when she gathered roots in the woods.

But presently all questions as to his course were settled for him.  His straining ear caught the faintest, almost imperceptible vibration in the air—­a soundwave so dim and obscure that it seemed impossible that the human mind could interpret it—­but Ben recognized it in a flash.  In some great trouble and horror, in the sullen light of that distant camp fire, Beatrice had screamed for aid.