Diana Wynne Jones 
Wild Robert [EPUB ebook] 

In the grounds of Castlemaine is a peculiar mound, hidden by yew trees. People say it’s the grave of Wild Robert…Heather finds the mound when she tries to escape the hordes of tourists who invade the stately home where she lives."Wild Robert, I wish you were really under there!" she cries. "You could come out and deal with the tourists!"All of a sudden, there is a smell like earth and strange spices. A voice says, "Did somebody call?"Heather gets her wish, and nothing is ever the same again!Wild Robert is a gentle, charming ghost, who is half a magician [on his mother’s side]. He returns after 350 years and is horrified by the antics of the tourists at his once home Castlemaine House. Since he’s a ghost who haunts by day, he plays some wonderfully wicked pratical jokes which drive the tourists away…