I first read this book 30 years ago. On finishing it this time I felt the same regret as then.
The theme is so bleak that it could be unbearable. It is kept from being so by three things. The first is the real possibility of good overcoming evil. The second is the ability of love to reanimate even the most hopeless situations. The third is the potential strength of the human spirit in such circumstances
Although its setting is most unusual, the characters are easily recognisable. They might have become stereotypes. Happily they are all too human for that.
This is a wonderful, if desperate, book.