Hell began with a song.

Deep, within the darkest prison, in the clutches of a cell old as Equestria itself, a fossilized prisoner sang. A sorrowful aria that begot Hell. The melody which stole away a Princess.

Ancient evils turn and nip at Equestria. Greenhorn soldiers go to war, mothers clutch their foals tight in fear for their lives, and mighty rulers of countries both near and far don armor bloodstained from battles past.... all because of an old mistake.
Because of an old mistake, Twilight is stolen away.
Because of an old mistake, a dragon marches, alone, away from all who know and love him, through distant, extraordinary lands and meets curious characters with one question on his mind:
Why?