Alright let's pick this one up right from this blog entry here. If we were to go back to the Hyperborea rpg for a moment then let's assume that the third edition adventure the Trapper's Lament has been completed. Now what?! Some of the player's PC's may have died but the rest will have gone up several levels. So it's time for me to unveil MM#7 Dread Swamp of the Banshee by Alan Chamberlain, Mark Taormino, & Joe Pearce
The basic adventure plot is fairly straight forward; "Downstream from the village of Silt is a great marsh created by a massive flood long ago. Many treasures were lost and now lay buried in the ruins of these cursed and water soaked lands. There are rumors that smugglers and criminals hide their felonious activities and great wealth here, but there is more to fear in the mist than the designs of men. Something sinister lurks in the darkness of the bogs. Find your courage, sharpen your blade, and trust no one and you may just survive the Dread Swamp of the Banshee."
This can easily be folded into either the Hyperborea rpg or the Castles & Crusades rpg system as is. There doesn't have to be a massive reason why 'The Banshee' is killing folks. It could simply be that she has awakened after the events of the 'Green Death' and is hungry.