Twilight Sparkle has cast loose the magic of Equestria and has been corrupted into a being that craves knowledge, no matter the cost. So, it’s up to Sunset Shimmer to save the day, right? Yeah, about that…
Sunset moves into her new duplex, but her roommate seems like she's a bit on the 'strange side'. Or more accurately, the 'completely psychotic and probably into all the crimes, all of them', side.
Sunset Shimmer is having a bad night. She turned into a demon, was forcefully turned back, and now has to deal with all the people she's wronged in the past. As luck would have it, it seems her demon self isn't done with her, either.
Love Tap has a reputation for being excellent at taking care of children. Twilight needs somepony to help look after the sirens. These two things really shouldn't have any connection, but desperate times call for desperate measures.