A regenerated King Sombra has declared war upon the Crystal Empire to reclaim it once again, this time backed by a formidable army led by a mysterious pegasus.

Unfortunately, the Empire's military is still ill-suited for open warfare and has to turn to Equestria for aid. All seems lost as everypony from the Element Bearers to Ponyville's mailmare is set on the front lines to fight a losing fight. But Celestia always has a backup plan.

When a retired P.O.N.I.E.S operative named Steel Pteryx is brought to the fight, he proves again and again to be the hero everypony needs. But Steel's dark condition continues to plague his every move, and may just be his downfall...as well as the Crystal Empire's...