Frank tightened his grip on the revolver. The animal was preparing for a rush.
The gaunt grey form gathered itself together and came directly at him.
Frank pressed the trigger.
The revolver crashed forth, awakening thunderous echoes in the narrow tunnel. The wolf gave vent to a howl of pain and fury, but although its onward course was checked for a moment and it swerved to one side it did not fall back. The bullet had not found a vital spot. Maddened by pain, the animal came on again.
The boys scrambled back. The wolf leaped. Frank flung himself to one side and the great body brushed against him. He struck out with the revolver and felt the weapon strike against flesh. Again he pulled the trigger, with the barrel of the weapon directly against the animal's hide, and then he sprang farther back into the tunnel.
Behind him he heard a shout. It seemed curiously far away. He retreated another step.
His foot did not find the solid rock. Instead, he stepped back into space. For an instant he wavered, clutching vainly at the air. Then he lost his balance, staggered backward, and then felt himself falling on downward into utter darkness.
CHAPTER XXI
Underground