The three princesses were just doing their duties as princesses, when they're visited by a mysterious stallion. The stallion tells them that the entire world is going to be plunged into an endless sleep, and that there's another alicorn in Equestria. Before the princesses could ask him anything, the stallion vanishes.
Meanwhile, Shimmer has just moved to Ponyville, and is trying to get accustomed to everything. However, it's not easy to keep her secrets, what with all the nosy ponies and surprise parties. But everything turns to the unexpected when Celestia is looking for a fifth alicorn, and dark creatures start attacking Equestria, putting everypony into a sleep from which they don't awaken! Shimmer is the only one that the sleeping spells don't work on. Suddenly Shimmer is the only one who can stop the new evil. And if she fails to save everypony, the whole world will end up falling into an eternal slumber.
OhwowsocoolIwanttoreadmore.
Why is the coverart of Lyra?
3080808
The first victim perhaps?
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NOOOOOOOO!! D:
3080160 Thanks, I'll try to update as soon as I can! :D
I'm confused. Shouldn't the Princesses' reaction be more firm? I mean, the Strange Visitor happened to kill some of their guards, and everything we have is Luna's that's terrible. Twilight also acts illogically - I think that in case of danger she'd go straight to the source to neutralize it, yet she just casually comments on the matter. And Celestia? What happened with her usual "I will protect my subjects no matter what?". For me, the scene lacked a typical "You'll pay for what did!" reaction.
Don't get me wrong, it seems that you can get a nice story of it - there's just enough mystery to make the reader interested. And my slight rant above is most likely caused by me reading a story built around Royal Guards about half an hour ago. I just felt bad for them, so if you could at least mention their bravery or describe their deaths as a great loss for the Princesses, it would really soothe my mind. And once again, it's not really your fault, I just happened to stumble upon your story after some deeper pondering over the guards as actual characters, not just plain minions.
3087425 No problem, I love feedback!
I was thinking the same thing with the Twilight saying that so casually. Even when I typed that part, I was thinking, The heck? Why would anyone say that when some guards were just freaking KILLED? But at the same time, I wanted that put in the story, 'cause I'm all weird like that. 
But I will change that part.
As far as it goes, she seems alright, but to be honest, it had only been four chapters. Wait until a few more before we can properly judge Shimmer's personality. But, like I said, she seems alright so far.
One thing to note: Celestia did not transformed Twilight into an Alicorn. She ascended on her own merit. Celestia just greeted her in that little 'dimension' (best way to describe it) and explained a few things for the most part.