Once upon a time, there were three young mares who went to the Guard academy. And they were each assigned very… hazardous… duties. But I took them away from all that, and now they work for me. My name is Blueblood.
Midnight, a reformed changeling, finds a job and a home with Twilight Sparkle. Now in the messed up town of Ponyville, she has to overcome mental disorders and make friends all while keeping her real identity a secret.
this is going on my read later list.
Hmm...good story. but there's need to be MORE!
The reason she wasn't corupted is pony have pure souls.