Corruptibility
I've always found J.R.R. Tolkien's Lord of the Rings to be something of a comforting read: a story that's a fun and exciting adventure, but with layers and layers of depths and moral clarity that's helped it stand up for the last seven decades.
I've re-read the books several times over the years, and last year, picked up Fellowship of the Ring on a lark and ended up getting sucked into it. The same thing happened recently while I was searching for something to listen to, and ended up starting The Two Towers (narrated by Andy Serkis.) I've been listening to it off and on in recent weeks, and just finished Chapter 6: The King of the Golden Hall.
It's one of those memorable scenes from Peter Jackson's adaptation as Ian McKellen's Gandalf goes up against Brad Dourif's Grima Wormtongue. I've always found this scene to be an interesting one, because it's such a neat example of how Tolkien critiqued power throughout the trilogy: it's very much a parable about the fragility of humanity and how easily we can be tempted by power.