Luna's sick-extremely sick-with something that Equestria hasn't seen before. Celestia, even after sending Twilight and Starlight to find a cure, feels like she isn't doing enough. Reluctantly, she teams up an especially eager Discord. And Nightmare Moon might as well come along for the ride-since she just watched a changeling die from the very same disease.

Meanwhile, Thorax is battling a strange fear of spontaneous combustion, but he's sure Spike won't blow up any time soon (Right? Right?!). Chrysalis and Cadence somehow end up trapped in a cave together. No comment.

Mixed up in all of the chaos, drama, and potentially dangerous villains lies an even bigger threat. Can Celestia, Nightmare, and Discord fight the incoming disease? Will Thorax actually come to terms with what he's really scared about? Will Cadence and Chrysalis actually start getting along for once?

Of course not. After all, this is Equestria crazier than before. And it's about to get even more messed up.