In our last volume Arc was sent to Tartarus for a crime he did not commit! Upon arriving he met and befriended a young dragon named Ember. Having nowhere else to go, he joined a community of ponies whose ancestors had been banished there generations ago!
Meanwhile, Twilight discovers her mistake in banishing an innocent human to such a hellish land, and proceeds to search for a way to rescue him! The Mane Six aid her in this task as they make their way to Canterlot Castle's library. Twilight approaches the princesses about the matter and is told they have an item that can be used to lower the barrier surrounding Tartarus! However, Princess Luna deems the task too dangerous and scuttles their rescue plan!
Ember falls ill with a strange illness which forces Arc to seek out the fabled hydra for its legendary humor! Defeating the Marquis, Arc is given the humor along with a number of the creature’s scales with which he can forge new armor! Ember recovers as Arc collapses from exhaustion! Her and Mythic Honor spend the night forging a new suit of armor for Arc as he rests.
The next morning Arc dons his new armor for the first time as Ember challenges him to ascertain his worthiness. As expected, Arc defeats Ember and proves himself worthy... of becoming her mate! He declines, as does not feel the same about Ember, nor will he be alive when she comes of age to wed.
Twilight and her friends march toward the Gates of Tartarus when a large portion of Ponyville to extract Arc from Tartarus by using a strange crystal given to them by a strange glowing creature of unknown origin. Amethyst Star organizes the defense as Twilight enters Tartarus alone under a magic cloak to render herself invisible. She spots the Vile Tribe's hideout and rushes there! Meanwhile the lord of Tartarus, King Malevolence, leads his army to the gates in an attempt to escape and bring about ruin to Equestria and its leaders!
Arc leads the Vile Tribe out along with Ember! As the brave defenders wane, Princess Cadance arrives with her own army of Crystal Defenders to aid in the effort! The Spear of Hope is returned to Derpy's hooves and she reascends as a Templar to fight against the demon horde! She along with Ember fly in to carry an overwhelmed Arc back to safety. He drops next to Rarity, grabs the crystal and smashes it to allow the barrier to reform. Unfortunately, Twilight is caught on the other side! As her friends watch helplessly, Arc charges back into Tartarus to save the one who banished him! Grabbing her, Arc dives back through the barrier (more on that in a later volume) back to safety. Turning, he sees his friend the Marquis being set upon by the demon army! Returning again into Tartarus, he gives the hydra time to escape. The King and his minions surround Arc and laugh at his situation. They are unnerved when he joins them in their revelry! When asked why, he answers by using Ember's Spear of Courage to let loose a shock-wave that decimates the army! Allowing the king to live, Arc turns and leaves to the cheers of his friends and the citizens of Ponyville!
That night, Arc approaches Twilight and official forgives her for sending him to Tartarus. The pair return to the Mane Six and Princess Cadance around the campfire as Arc is informed that he is entitled to a Royal Decree for his actions! The princess hands his a scroll on which he is to write out his heart's desire. She accepts the request and Arc is granted his freedom along with full, legal citizenship in Equestria.
However, many questions remain unanswered. Who was the bright creature who helped Twilight by giving her the strange crystal? Who is the creature in the black cloak with the glowing eyes? What will the Vile Tribe do now? How will Ember acclimate to life in Equestria with her "fiancée", Arc? But... the biggest question of all...
...what will Arc do with his newfound power and armor? Time will tell. Sooner or later... time will tell...