(To avoid confusion, the cover art was simply the best I could find involving superhero Spike. If anyone knows of any good fanart involving a superhero Spike that isn't Power Ponies, please link me to it)
For as long as Spike can remember, his past has been a mystery. A puzzle without a solution. In short, he has been left with many questions, that no one seems to have the answers to. All he knows is, that he strongly believes in the concept of justice, and that ponies are inherently good.
Then, one faithful day, he is called to Canterlot to meet with Princess Celestia. And upon learning the truth of his past, Spike decides the time has come for him to embrace a role beyond that of an assistant.
Before long, all of Equestria is struck with awe at the arrival of a new superhero. And the question on everypony's mind is "Who's behind the mask?"
It's a question that will motivate one pony to issue the ultimate challenge, to see whether or not brains triumph over brawn. And challenge Spike's faith in Equestrian civilization.