The Girl in a Swing, by Richard Adams, Alfred Knopf, 1980.
I found this book at a second-hand story. I remember reading Watership Down -- at least thirty years ago -- and liking it, so, for a dollar, I picked up this book.
This book is not really very much like Watership Down. But the writing is still gently beautiful, as the plot becomes increasingly intense. By the end of the book, I, like the protagonist, did not want to believe what I know.