for The Bagpiper's Ghost by Jane Yolen
On a midnight visit to a Scottish cemetery, Peter and Jennifer get caught up in a drama three hundred years dead--a tale of two star-crossed lovers and the man who betrayed them. Their bitter ghosts still haunt the graveyard, too angry to leave the world of the living . . . but all too willing to drag Peter and Jennifer into the world of the dead.
Publisher description retrieved from Google Books.