Characters’ motivations are unclear throughout, their emotions are heightened and complex, and, in addition, Isobel English (actually a pseudonym adopted by June Braybrooke) has a healthy respect of the unknown. There is at least one scene in Every Eye in which readers are given to think that a spirit has presented itself.
But, at the subject matter reveals, what is known is often every bit as confusing as what remains unknown.
In all, this makes for a curiously unsettling read. But in a good way.
More here (but still spoiler-free), if you're interested.