A potential plot by disenchanted nobles to overthrow the princesses is discovered by Equus, the clandestine agency headed by Princess Luna herself. Restricted by the laws that govern the very land she is dedicated to protecting, she is forced to seek out the aid of one who can operate outside the rule of law - Fairlight, a former watch officer and last living descendant of the tribe of wendigo. With his help, Luna and her agents must act quickly to help track down the plotters and bring them to justice before they can attack the royal wedding. But helping the princesses comes at an unforeseen cost that pushes Equestria towards the brink of all out war with an ancient foe, and takes from Fairlight that most precious of gifts - his own son.