Tirek is summoned by an optimistic Celestia, in hopes of at least making amends to their currently bitter, enemy relationship. Will Tirek be open to Celestia's preaching?
Does he have a choice? Maybe he's needed for something important! Like writing better summaries! We'll see!!!

Words have worked to reform other villains, but, as everypony knows, centaurs are stubborn and Tirek also has a wonderful way with words...but maybe certain actions will show and shine through his dark, never-changing mind.