Houston," called out Frank to the approaching rig, "there's a man over yonder annoying this boy and trying to rob him." "Is, eh?" cried the officer. "Whoa!" and he arose in the seat to get a good view of the spot toward which Frank pointed. "I reckon he's seen me, for he's making back his trail licketty-switch." "Keep your eye on him so he won't follow us, will you, Mr. Houston?" pressed Frank.