After the events of The Magic and the Night, Luna has been developing an attraction to Twilight, but is having trouble expressing it. Complicating matters is that Twilight misses Flash Sentry from Equestria High. As Luna attempts to grow closer to Twilight the Crystal Empire declares war on Canterlot. Using ancient magic of unbelievable power, Cadance is invincible. The only hope of defeating the new Crystal Empire is King Sombra's knowledge of forbidden magic. If he can be revived then he can lead Twilight and Luna to his hidden laboratories deep in the frozen north, but Cadance is determined to get there first. What happened to Cadance to make her change, and what will the cost of Sombra's help be?