I heard Chapter 12 starts a new story. Who is it about and how is it introduced?

Yes, the latter part of Chapter 12 sets the stage for what it calls a "very delightful story" meant to illustrate the Guru's greatness. The story's protagonist is introduced as a ritualistic and orthodox Agnihotri, a keeper of the sacred fire, from the holy city of Nashik. His surname was Mule. The chapter explains that he came to Shirdi not by plan, but due to a fortunate coincidence brought about by the strength of his past merits. The text makes a point that one cannot even stay in Shirdi for a moment without such merit, highlighting the spiritual significance of being drawn there.