Frustrated with her sister's free spirit and new adventures, Luna resolves to find something new to live for, now that she is retired. The answer: A power metal band. And who better to join her on her quest than the Nightmare Knights?
Equestria faces its most dire threat yet as Grogar and his legions march upon Canterlot. Meanwhile, Cozy Glow, Chrysalis, and Tirek prepare to betray him and seize power themselves. Can the Mane 6 save Equestria?
Cozy Glow has been locked away in Tartarus as punishment for her crimes. There she meets her pen pal and new neighbor, Lord Tirek. She then proceeds to drive him completely nuts.