The Wonderbolts are a famous stunt organisation, but not many know of their secondary function - the second most advanced military force in Equestria.
When an unknown threat arises that could not only reveal this secret to the public, but also wipe the Wonderbolts out and pave the way for an invasion of Equestria, Princess Luna sends out her secret military project - the Ghost Squad, led by her personal protégé - to deal with them
However, there's more to this threat than any could have known, and Luna may have just put her protégé and his squad in serious danger...
EDIT: Dark tag added because of chapter 5