Moonstone Ruby was an alicorn.
Kind of rare in the Fillypines. She is sent to an alicorn school at the palace, and learns the trade of being a queen, even though it is very unlikely she'll ever be one.
But she has this thing. It's called curiosity. She's always had it, and now it has lead her to read some books about a mysterious and forsaken isle. When she learns about a lost explorer, a mysterious pony called, "the Dark Pony" and strange happenings, all on that isle, she must find out what's going on. So she goes to the island and finds herself in a race for her...and some pony else's...life.