It's the aftermath of "Alicornundrum." Twilight, Ink Spot, Spike and Nyx are back in Ponyville, the library is undergoing renovations to accept its expanded (and somewhat more royal) family of tenants, and everything is back to normal. Nice. Quiet. Peaceful.
And then Tirek escapes from Tartarus. The fool.
This is, of course, an unofficial alt-universe fanfic sequel to "Past Sins" by Pen Stroke.