From the introduction:
For decades, Osken's Point has defended a small pass through the Graywall Mountains. Once, it defended Breland's western borders against monsters, raiders, and other threats. Today, it is one of several forts that forms a defensive chain between the monster infested land of Droaam and the kingdom of Breland. Well stocked with supplies and staffed by several hundred skilled soldiers, the Point has served its duty well.
Recently, a new threat has arisen to menace Osken's Point. A mighty green dragon, intent on uncovering an artifact called the Heart of Reason, has recruited a small army of orcs, ogres, and other monsters. Dubbed the Army of the Wyrm, this ramshackle force has gathered in secret to destroy Osken's Point. Even worse, the dragon hired a half-orc spy to enter the Point, contact its chief siegemaster, and offer him a massive bribe in return for his service. The greedy siegemaster accepted the spy's offer. He sold the dragon plans for the Point, along with maps of the tunnels and sewers beneath it. Osken's Point was built atop an ancient fort, one that had a number of tunnels running to a variety of caves throughout the Graywalls. One of these caves holds the Heart of Reason. The dragon has already uncovered this place, and he is now poised to seize it.
Luckily for the folk of Khorvaire, the dragon cannot yet claim the heart. When Osken's Point was first built, the engineers found a strange, green staff amidst the rubble. Divinations and other investigations linked it to the heart of reason, but no one was able to track it down. The dragon must seize the staff to open the vault containing the Heart. The siegemaster, while unable to steal the staff from the commander's vault, has given the dragon the next best thing. The dragon sends the bulk of its army to attack the Point from above, while a small, elite unit uses the siegemaster's maps to attack from below. By catching the defenders from two directions, the dragon believes that its victory is assured.
The Siege of Osken's Point is provided as a 14-page PDF scenario and a 2-page DOC errata; with an additional 4-page DOC handout (print-and-play).