The Minotaur by Barbara Vine
I've never read Barbara Vine, the alter ego of Ruth Rendell (whom I've also never read), but after seeing blurb after blurb about her fantastic writing, I grabbed one of her books off the shelf and began reading.
This mystery/suspense novel is very much about the "why", rather than the "whodunit". For three quarters of the book, there is little action, just a slow build to what you KNOW is going to be an almost inevitable end, but which is still surprising. This is definitely a character-driven novel, focusing on Kristen, a newly-hired "caretaker" for John, a 39-year-old man considered "mad" by his family, who are themselves not exactly the picture of mental health. Taking place in Britain in the 1960s, the reader quickly recognizes autism, rather than madness, in John's actions, but so many years ago, it was a different story.
I was pulled into this story, and despite initial misgivings, found it a great piece of suspenseful literature. Recommended!