The Red Judge by Pauline Fisk. 202 Pages, Finished 8:04 p.m.
Odd mix of fantasy / not fantasy / not quite magical realism, either.
Zachary/Zed Fitztalbot feels responsible for his older sister's accident; and his father also blames him, and dumps him at the abandoned house of his recently deceased grandmother.
It's unclear how much of the next week or so Zed dreams, imagines, or is real; Welsh myth and legends come to life, reality changes, as Zed confronts his own guilt about his sister, his failure to fit into the Fitztalbot family, and questions about his own past.
It's something I need to reread when I have more time, to try to work it out. Because it's neither straightforward fantasy nor real. Apparently, part of a trilogy so I need to look for those other books. I'm reminded of both Alan Garner & David Almond.