What mistake does David make when he asks Neil Roy about Alan Breck? How does it all work out? From chapters 13-16

He asked for information on Alan Breck, offering money. Macrob was deeply offended. David then showed him Alan's silver button which Macrob recognized. He chastised David for not showing this first and grudgingly gave him Alan's instructions. David was given a route which led from the inn at Kinlochaline to Morven to Ardgour across lochs and finally to the house of James Stewart of Appin. Macrob warned him to speak with no one.