Eternis is under attack. A vast and powerful mul incursion threatens Runethedian's oldest city. Legion, his half siblings Dauge and Dusk, along with other heroic allies both new and old come to answer the ancient city's call. But the mul incursion is only the beginning. Once the incursion is thwarted and finally put down, diseases begin to spread across the southern pantheon of Runethedian. With the risk of the diseases eventually spreading upward towards Eternis, eight heroes, mostly veterans of the war come together in hopes of stopping the diseases. It is soon learned that the key to their success lies within their own walls. Slate Thundershot, an Eternian who is an alleged time jumper from a time now long gone has left behind journals with information that proves pivotal to the heroes. His descendent, Titus Thundershot eventually joins the crew with a band of heroes of his own. Together, they embark on treks that take them to places unseen by civilizations for thousands of years. One particular island has never before been seen except by those that lived there. The kingdom of Thox is ravaged by the diseases which in turn forces internal conflict. An ancient entity that was once locked away proves to be the catalyst behind the diseases. As they continue to spread, our heroes drive inward to the heart of it all. In the end, not all are standing. Some will fall. The few that are will never be the same. Some are even left behind. In Thedia: Book of Heroes, two bands of brothers become one in a common goal to save not only Eternis but possibly the entire southern half of all of Runethedian from an ancient entity's involuntary action; the bleeding of diseases to the open surface world of Thedia in the Runethedian pantheon.