From "Adventure Background and Summary:"
The wall of the gods has long protected Onara from land-based incursions of the unbound infernals that resided behind the hills. A little known phenomenon known as the Wall of Yarris prevented ships from reaching the shoreline past the Wall of the Gods, and ships from leaving the shoreline there. However, when the Wall of the Gods fell, so did the Wall of Yarris, leaving the seas of Onara open at last to these infernals.
Not too long ago a band of dangerous infernals and the tainted ones who worship them struck out on a fleet of warships. They have been traveling down the coast of the Hinterlands, raiding and slaughtering wherever they may.
The adventure starts with the PCs just arriving at a small Hinterlands village, to find it destroyed and burning. In the distance can be seen the Infernal fleet sailing south. There are several options that the PCs have, they can attempt to hunt for survivors, they can search for a vessel to follow them in, or they can simply chase them on horseback.