It is interesting that as soon as the people of Lehi fled to the camp of Moroni, the people of Morianton who were causing all of the trouble were terrified that Moroni would sweep down upon them. They therefore decided to cross the narrow neck of land and flee into the land northward where the bones of the Jaredites were scattered in total desolation.
Of course, Moroni was most anxious that the land northward be protected from any settlement by people antagonistic to the Nephites, but his defenses were aimed at the Lamanites. As a result, Morianton's scheme would have been secretly carried out with complete success had not one of his own people advised Moroni what Morianton was planning. Here is how Moroni learned about it.