Chosen answer:It's not a ghost. It's a patronus, like the one Harry conjured in "The Prisoner of Azkaban," to save Sirius Black. Every wizard's patronus takes a different animal form. An as yet unknown ally (revealed in part 2, and the book) sent the doe patronus to lead Harry to where the Sword of Gryffindor was hidden.
Chosen answer: It's not a ghost. It's a patronus, like the one Harry conjured in "The Prisoner of Azkaban," to save Sirius Black. Every wizard's patronus takes a different animal form. An as yet unknown ally (revealed in part 2, and the book) sent the doe patronus to lead Harry to where the Sword of Gryffindor was hidden.
raywest ★