It's been a few years since Tirek's defeat, and due to an oversight on Princess Sparkle's part (or possibly Mayor Mare's, but that's up for debate between the Princess and the Mayor to this day), Ponyville was left without a public library. Oops.
Everypony knows about Pinkie's 'Pinkie Sense'. She's saved many a pony from calamity, often with hilarious outcomes, and Pinkie is ok with that. So long as nopony suspects that there's something else happening; something dark that Pinkie is hiding.
We all know what’s been going on with the Main 6 and Tempest while they were away from Equestria. But, the biggest questions would be: What happened while they were gone? What could the Storm King have done while he took up residence in Equestria?