The plot was interesting, although as with most of my dreams it doesn't make much sense when I sit down to try to explain it. I'll invent a few details in an effort to fill in the gaps of either the dream or my recollection of it.
It started with an impoverished young woman/girl and a wealthy family at a mansion. The young woman had been taken in by the wealthy family as a poor relation, but she didn't fit in. They treated her badly, especially the young brother and sister who were about her age. Sometimes they'd harrass her, and other times they treated her as if she wasn't there. She prefered the latter, being ignored, and started willing herself to be invisibile and insubstantial. Gradually, she receded from the physical world, turning herself into a ghost. She remained at the mansion, haunting her erstwhile tormentors.
Time passed. The children grew up, married, had a child of their own. (If this were a real story, the brother and sister would've, one presumes, married other people. In the dream I'm pretty sure they married each other. Well, it keeps the cast together, I guess). But they remained at the mansion. The ghost was still around but not much seen, until one day when the parents were out in the garden with their now-teenaged daughter and saw the ghost, reading a book. Offput by this sight, the parents attempted to withdraw, but the ghost advanced on them with a cold expression, insubstantial and implacable and frightening to the adults.
The daughter, however, was intrigued by the ghost's book. She'd never seen a book before. (Apparently she led a very sheltered life.) She stole forward and attempted to tip the book from the ghost's hand. The ghost, startled by this boldness, dropped the book. The daughter fumbled an effort to catch it and it fell to the ground. The daughter promptly burst into tears, convinced she'd broken the book and full of regret both over the book's "destruction" and for her own part in it.
The ghost, who'd not aged and still looked like a young woman, became fascinated by the daughter after this. The parents were horrified and wanted to protect their daughter from the ghost, but they couldn't stop her. The daughter, in turn, was attracted to the ghost. At a later point in the dream, the ghost brushed past the parents to approach the girl and became solid enough to kiss her.
Gradually, the roles of the ghost and the parents reversed: the ghost became real and solid again, and lived in the mansion with the daughter, while the parents were forced into an insubstantial and impotent existence.