Tomb of the Overseers is a d20 System scenario for five to six 3rd- to 5th-level characters. Part of AEG's Adventure Keep line of short, cheap modules in half-sized format (4-1/4"x11"), it is intended to be run as a single session. From the back cover:

Nearly 100 years ago, Lord Eriador wrested the lands from the hands of evil and began a reign of unsurpassed courage, wisdom, and might that lasted over three centuries. One day this great man of valor was called onward to continue his battle for freedom and goodness on a higher plane of existence. Leaving the responsibility of rulership to his faithful overseer, he donned his magical shield, helm, and sword and traveled to the Holy Mountain of Anduin to meet his destiny.

Eriador left the overseer with this solemn promise: if there ever arose a time of great need, he would answer a summons from the Mountain of Anduin to come back to vanquish any evil that dared to oppress his people.

It is now the reign of the third overseer. For years now, an evil mage has been plaguing the land by sending forth hordes of evil humanoid minions to oppress the people. The overseer has been forced to pay tribute to the mage to protect his people. Life has become nearly unbearable for his subjects.

It has been over five years since the mage desecrated the holy mountain by placing foul creatures in its depths to guard against the possibility of the people seeking help from their nearly forgotten champion.

A fortnight ago, your party was gathered in a secret council chamber to meet with the overseer himself. You felt a spark of hope for the people of this land as the overseer told the legendary tale of Eriador. He gave you the equipment you would need and charged your party with the task of venturing into the heart of the now monster-infested Mountain of Anduin to call back the people's great hero, Eriador the Paladin. Although the three parties sent before you had not returned, ridding the land of the mage seemed worth any risk, and you eagerly set out on your quest. Now, standing before the defiled mountain, you wonder if perhaps you were too hasty.