SOLUTION The moon was well down toward the western edge of the prairie when the boys rode away from the bunk house.

They rode toward the south, in pursuit of the bandits, as they now called Whiff, String, and Ham.
Whitey and Injun had settled on this course shortly after Whitey had decided that the men were intent on train robbery.

There were several reasons for their choice.
For one thing, it was too late to go and warn Bill and the other punchers at the Junction.

And even if it were not, if they did that they would have to share with the ranch men the glory of the pursuit and possible capture of the bandits.

It may have been rash of the boys, but after their former adventures they felt capable of taking care of three bandits by themselves--especially if they came on them unawares, which they intended to do.