User Note: For characters level 7-10.
From the introduction:
The Temple of the Iron Codex was buried thousands of years ago by heroes who thought to keep the power of the Codex safe from any who would try to read it. So long as the Codex remained safely within the warded area, covered upon its altar, its power would never be released. However, if the Temple were disturbed or the book moved from its location, the malevolent spirits of the Codex would fight for their freedom, bringing horrible plagues and curses, until a great evil came to free it from its prison. To further guard the Temple, it was buried deep beneath the group, where no one could ever find it. All traces of it were destroyed, all maps were destroyed, and all legends of the Codex were lost...almost.
Centuries passed, and a city was built over the site of the temple, its inhabitants not knowing what lay beneath their homes. When an earthquake fractured the ground on which the city stood, the Temple of the Iron Codex was unearthed- and the gates to the Temple shattered. Deep within the passages of the Temple, the earthquake has shaken the book from its protections, allowing the evil of the Codex to seep out past the iron gates that once enclosed it safely. That city is the site of the current adventure- and we recommend that you make it your home campaign city, the safe haven for your adventurers. After all, what better motivation for your characters than to save their own home?