If you've been with us for a while - like, since the beginning of the Library - you'll remember that our first review ever was by yours truly, on the inimitable Howl's Moving Castle by the sadly late Mrs. Jones. My estimation of her work has only gotten better now that my biggest book collection is of her books, and my only complaint is that she isn't more widely read in the US. (Not sure about the UK.)
Now about The Time of the Ghost instead of mindless fangirling.
She doesn't know who she is, and doesn't know why she's invisibly floating through the buildings and grounds of a half-remembered boarding school. Then, to her horror, she encounters the ancient evil that four peculiar sisters have unwittingly woken - and learns she is their only hope against a deadly danger.
I gave you the summary from the back of the book because you really shouldn't go into Ghost knowing too much about it. The fun of Jones's books is learning alongside the main character, and that's especially true in this book. Ghosty (just calling her 'the ghost' is so cold, isn't it?) is completely clueless, and I can imagine that it wouldn't be half as intriguing if you aren't, too. Therefore, I won't go too much into plot or individual character, and therefore, this is going to be a very short review.
BUT! I'm not going to let you go with some more fangirling, so I am going to expound on the general plot and characters.
The plot is, as I said, a bit confusing at first, because you have no idea what's going on. No idea. It's confusing, it's bewildering, and you can feel exactly how Ghosty feels. And though you eventually get your sea legs, to mix my metaphors, there are still points where you scratch your head and think, 'But I thought it went THIS way...' And then you have to scrap your preconceived notions about the lot of it and start again.
Which, for me, is just fun.
The characters are typically amazing for Jones. None of them are quite what you think they are at first or second or even third glance. Ghosty, for the most part a mere observer in her quest for victory over the ancient evil, is a pretty interesting main character. The 'four sisters' mentioned in the summary are a wild, varied bunch of witches that would make Macbeth's hags run away in terror, but at the end of it all, I actually really liked all four of them. And the two villains, though extremely different, are both detestable, and you dearly want them both to go die in a hole by the time the book ends.
Oh, and that ending is wonderful. Just so you know.
There's very little I can say against The Time of the Ghost. Maybe that one character swears a bit more often than is typical for a Jones book? It's still not bad. In other words, go read this book. And all of her others. Because Diana Wynne Jones is amazing.