While performing an inspection of Tartuarus for Princess Celestia with her friends, Twilight is paying homage to one of Equestria's greatest foes: The Lich known as Dead Horse. Upon arriving, they find the Cerberus dead and all the signs that Dead Horse has escaped. Princess Celestia summons her allies; but she finds that even the combined power of Discord, Shining Armor, and all four Princesses cannot defeat Dead Horse. She accepts that, with the Lich using her own ancient magic against her, only the Rainbow Powers can defeat him. As Equestria falls to the undead armies, Twilight springs a trap in a desperate attempt to bring Dead Horse's attack to a close.

The Summer Solstice is fast approaching, and everypony is gearing up for the annual celebration. But everything is threatened when Braeburn arrives in Ponyville with terrible news. A swarm of Cries O'Melody Beetles is sweeping across Equestria. It is eating all the vegetation everywhere it goes. And according to Twilight, no such swarm has ever been stopped by ponykind. But another erudite pony, Bookkeeper, suggests that Hedgehogs may be the key to stopping the advancing swarm. Twilight, Fluttershy, and Bookkeeper venture into the Everfree Forest to acquire a sounder of their own, save Equestria, and keep the celebration on track.