It swept around the bend at perhaps a hundred miles an hour, stretching from wall to wall of the canyon, the crest of it seething and slashing and towering forty sheer feet above the canyon’s floor.

A prowler was running in front of it, running for its life and losing.

There was no time to watch. He leaped upward, as high as possible, his crossbow in his hand. He caught the end of the bow over one of the sharp projections of rock on the ledge’s rim and began to pull himself up, afraid to hurry lest the rock cut the bowstring in two and drop him back.

It held and he stood on the ledge, safe, as the prowler flashed up the talus below.

It darted around the blind-alley shelf and was back a moment later. It saw that its only chance would be to leap up on the ledge where he stood and it tried, handicapped by the steep, loose slope it had to jump from.