Suddenly his fears were wiped away. Na appeared at the point he watched. She burst from the woods, running swiftly. A few seconds later, five rat men came into sight. One of them carried a ray gun.
The running figures looked tiny from the height of the cliff. They would make very poor targets. But a glance at the narrow point below reassured Ro. Even if the stones went wild, they would still land in that small area. There was no chance of their missing.
Na had entered the narrow strip. She seemed to be tiring. The rat men gained. Ro bit his lower lip and clutched the stones in his hands more tightly. Carlson crouched behind the larger rocks and boulders, ready to roll them over the ledge.
The rat men entered the pass.
Na had already passed below and was almost to the end, when she stumbled. Her head struck the hard ground as she pitched forward and she lay still.
Ro's heart leaped in his breast.
"Now!" he shouted, and let fly with one of his stones.
The missile left his hand with terrific speed. All the frantic strength in his arm was behind it. It flew straight to its mark. The Oan carrying the ray gun dropped like a log.
Carlson shoved the heaviest boulders off the ledge. He worked furiously, moving from one to the next. They fell like a thunderclap on the rat men below.
But Ro had given the signal too late. Three of the Oan were crushed under the barrage. But one moved too swiftly. He passed under the falling stones unharmed and raced toward the fallen Na.