He rose and stood looking at William for a few minutes, then took the lead rope and tied him to a juniper that stood near the spring.

The note had said that the last horse died down the canyon, the implication of mystery lying heavy behind the words.
Casey went back to the tent and read the note through again twice, studying each word as if he hoped to twist some added information out of it.

It sounded as though the writer had expected his partner back from some trip and had left the note for him, since he had not considered it necessary to explain what it was that he had seen again in a different place.

Casey wondered if it might not have been that strange light which he himself had followed.

Whatever it was, the fellow had not liked it.