A meteor impacts the nation of Equestria, Planet Equis. Tranquility is quickly snuffed out when a poison begins to spread violently. The Princesses cannot combat this unknown threat, as no knowledge of it exists. Help comes from an unexpected source.
MLP/Warhammer 40K crossover, part 5. The pieces are placed. The battle lines have been drawn. The 38th Company and Equestria fight relentlessly against the alien menace (the other one, that is), but the odds are hardly in their favor.