The Shade of Hettie Daynes

If you expect to see a ghost, you see a ghost...
That's what Bethan tells herself when her brother Harry takes her to see the ghost at the old reservoir. But she really can see it: a pale figure floating over the water, one finger pointing downwards.
Local legend says that the ghost is Hettie Daynes, an ancestor of their family, who vanished over a hundred years ago.
If so, what does she want? And why is she appearing now?
Harry and Bethan and their