The Doctor and Derpy travel to present-day Canterlot, where it happens to be Hearth's Warming Eve. Overall, everything looks about how it should be...save for one little filly that appears to be by herself in what should be a joyous time.
Discord's hold over Ponyville has been broken. Harmony has returned once again, and the Chaos he created has vanished...save for one of his more beloved creations. Now Screwball is out to create enough Chaos to release her Daddy Discord.
Whether we like it or not; time slips away from us. Sometimes we just want to forget that tomorrow's coming and remember yesterday. Even Discord does it.
Discord is convinced that while trapped stone he preserved a dangerous disease inside his body. Now that he's free again he's become convinced that those closest to him are at risk.
A cult of Discord worshipers learn of his reforming, and are disgusted with their god. Now they obey another spiritual deity...None other than Discord's spawn, Screwball...and she plans on finishing what her Daddy Discord won't.