With the advent of Cadence, the princesses have come into their full power, and they're just in time: the ponies' oldest enemy has teamed up with their newest to open Tartarus itself. While the princesses defend Equestria against endless armies of ravenous monsters, Twilight Sparkle and her friends embark on a desperate quest to find an ancient artifact that may be their only hope for salvation.

This is a crossover with G1, but should be comprehensible to anyone who hasn't seen the G1 series. Contains action violence, some intense situations, and sexual themes, but no graphic gore or sex.