Now that Fangheart has been tried, convicted, and sentenced, he's immune to any similar charges. Since his last trial was barely —if at all— fair, Twilight is looking to investigate Celestia's treatment of changelings and other emotivores.
Now that he's out of trouble for now, Fangheart wants full Equestrian citizenship and legal rights granted to himself, if not all changelings. And they may need it soon, as a plight is spreading through the hive, and changelings begin fleeing north to escape it.
But nothing is ever so simple. Fangheart gets... distracted, shall we say.

Rated Teen for kissing, changeling courtship rituals and (a) feast(s), crude humor, and zombie ant changeling fungi.