He said one soft word, "Promise!" or else Caius imagined he said it.

Caius knew at least what the boy wished him to do.
The pony moved nearer, shivering with cold, and Caius realized that the condition of wet and cold in which they were need not be prolonged.
"I promise," he shouted angrily, "and I'll keep the promise, whatever infernal reason there may be for it; but if I'm attacked from behind----" He added threats loud and violent, for he was very angry.
Before he had finished speaking--the thought might have been brought by some movement in the shadow of the cloud, and by the sound of the wind, or by his heated brain--but the thought came to him that O'Shea, under his big fur-coat, had indulged in strange, harsh laughter.
Caius cared nothing.

He had made his decision; he had given his word; he had no thought now but to take what of his traps he could carry and be gone on his journey..