Ryujin
Legend
I segued into Assault on Nightworm Fortress, from Revenge of the Giants, by having the party's mentor's soul not reach its final rest, at the end of the module. An Exarch of Moradin appeared to them, to tell them that his soul had not appeared before The Raven Queen to earn his final reward.
Souls are power and particularly rare, and influential people's souls could be presumed to carry more relative power. Was just one soul required, to fuel some sort of dark ritual or produce a powerful artifact, or is someone diverting a veritable swarm of souls in order to try and garner power over death, itself?
In this way you can make the soul just another MacGuffin, to drive the adventure you choose.
Souls are power and particularly rare, and influential people's souls could be presumed to carry more relative power. Was just one soul required, to fuel some sort of dark ritual or produce a powerful artifact, or is someone diverting a veritable swarm of souls in order to try and garner power over death, itself?
In this way you can make the soul just another MacGuffin, to drive the adventure you choose.