Shibumi, by Trevarian

The book, written in 1979, is less dated than I'd expected -- in that the cultural insensitivity (mostly picking on the French and Americans, of all things!) and the adolescent attitudes seem more a reflection of the author than of the times.

There's deep character development, at least for the hero, Mr Hel. But it stretches too far.

Out of curiosity, I checked the Amazon rankings: 75% of the 168 comments were 5-stars. In my view, that just means that 126 people were wrong.