A long time ago when the ponies were still separated in their tribes, unicorns probably thought of themselves as so highly. For they are the ones gifted with casting magic. Being able to control things at their whim made them feel so superior...

Though now, even though unicorns live amongst their non-magic casting peers there is a sudden illness befalling the magic casters in Equestria...

First it was just a few sparks of magic that come out. Then one day, it seemed like a freak accident. A random stallion, his magic causing an explosion of great force causing a collapse in a building. Multiple casualties and some survivors shaken. Now some other unicorns are showing symptoms, but not as note-worthy. These ponies want answers.