The Battle of Stag's Tomb and the Disappearance of Terras' Perfect History

Write about a myth or legend relating to a famous, long-lost item.
At the dawn of the Age of Gods, the time after Fezzeret was slain and before Cataclysm, the goddess Terras penned a magic book. This book, only readable by those learned in original languages of the 6 Gods of 4 Corners, contains a complete recount of every any event that has happened in 4 Corners starting from its formation to the present day. Its pages are neverending, its recountings are factual and perfectly accurate, and it actively and magically writes itself the moment another major event happens. People can learn of famous lineages dating from their very beginning to the most recent generations, of battles fought and won or lost and who participated in them, and most importantly how the most influential moments in 4 Corners history played out and the reasons why. 
3 Copies of this book were created, but only one copy remains on display where the public knows where it is. One was lost when the Severance came and the Great Earthquakes swallowed it along with the library that held it; the other copy was stolen from its place of importance the very next day. 
At the dawn of the era Post Severance, and the time leading up to it, the southernmost kingdom of the Northern Corner, Senchet, was led by the Serpentine peoples. The other 6 kingdoms of the Northern Corner felt uneasy with their leadership due to their partial fiendish heritage, but despite their uneasiness, Kingdoms of the Northern Corner worked in harmony. "Peace and Order through Awareness and Understanding" was the Northern Corner motto. And, they had yet to learn of any treachery, so therefore, it would be illogical to assume any. 
This kingdom was home to the Burial Grounds, a collection of elaborate tombs where most of the Northern Corner's most important monarchs were laid to rest. When Grand Monarch Keryneia Philia had tragically died and thought to be the last of her line, her remains were set to placed in her tomb along with her family's copy of the Book they had treasured and guarded with their lives so much. A grand funeral procession was held as the people mourned her until she was placed to rest in the beautiful octagonal burial chamber emblazoned with her family's crest of a 12 point stag. Everything went as scheduled and planned, it was the Northern Corner way, after all, and the Earth Touched, the Children of Terras, combined their magics together to seal the tomb at the end of her funeral. 
The next morning, the attendant who was to care for the monarch's tomb never returned. Then another who was sent to go find them. Then another. At last, a small unit of Brass Guard went to what was becoming of these people only to find the tomb's entrance destroyed and a collection of the Serpentine nobility corrupted by unknown magics and powers ready to attack, kill, and consume anything that tried to cross the Tomb's threshold. The battle was fought to a stalemate as more Brass Guard and soon magicians were called to help control the corruption. None of them had seen anything like it, and the arcanists called to assist the Brass who possessed the Sight could confirm, Keryneia's Tomb was not only desecrated, but her copy of Terra's Perfect History was gone. 
The Battle of the Stag's Tomb continued for a month, as the corruption was spreadable, like a phage. And as more of the Northern Army fell, more reinforcements for the Corrupted Serpentines would rise. It finally ended when a collection of Scarlet Knights arrived to cleanse it. Yet, no matter how hard they tried and how many times they tried to slay the Serpentines, they would simply rise again the next morning, over and over again. It was decided that a powerful warding spell, which combined the magics of the 6 Deities of Four Corners together as well as the magic of Land itself would be needed to seal the tomb, and the terrifying undying within. The spell was cast, and the tomb was sealed. Only a curse of a thousand generations would open it, and no thief nor leader would be desperate enough to open it.
But what of the stolen book? Who took it? Who caused the Corruption of an entire monarchy? All of these are answers that have yet to be found. And as for The Tomb of the Stag does it even exist? Only Terra's Perfect History could tell you for sure.