He didn't know, he explained, but what his cat Compadre was somehow involved.

He had stood in the shadow of his tent for a few minutes, and had seen Bill Holmes sneak into camp, coming from up the arroyo somewhere.
For some reason he waited a little longer, and he had seen a woman's shadow move stealthily up to the front of Annie's tent, and had seen Annie slip inside and had heard her whisper a command of some sort to the dog, which had immediately hushed its whining.

He hated to be telling tales on anybody, but he knew how keenly Luck felt his responsibility toward the Indian girl, and he thought he ought to know.
This night-prowling, he declared, had shore got to be stopped, or he'd be danged if he didn't run 'em both outa camp himself.
"Bill Holmes might have been out of camp," Luck said calmly, "but you sure must be mistaken about Annie.

She's straight." "You think she is," Applehead corrected him.

"But you don't know a danged thing about it.