The Black Cauldron, Book 2 in the Chronicles of Prydain by Lloyd Alexander
This is has been a fun series thus far! The teenaged protagonist is looking to do interesting things, like being an explorer and warrior, and has a changing quest but a familiar band with him across the two books. We find this time a very disagreeable youth who stands in as the main antagonist, who lies, insults and harms, but has occasional glimmers of hope when he does the right thing - but when it suits him so.
I'm looking forward to reading the full protagonist character arc, as he is showing signs of maturity and a desire to treat others fairly - even those that do not extend the same to him. I'm not sure I would have been too kind to the antagonist in the same way. However, we all have character flaws, and one of mine is not extending a lot of grace to those I feel are acting appropriately.
I guess you can learn something from children's books.
I'm looking forward to reading book 3 over the weekend!