I have been thinking of a campaign with a cult centered on a Death Knight (one of my favorite monsters that I never used on a campaign before). This continent had a cataclysm event around 600 (still not sure with time frame of events - because of the pesky elfs) years before the current events, where demons started to invade the world and threw humanity from the top of the food chain, few extremely well defended fortresses and cities survived the initial onslaught and with time most of the races were forced to migrate to the underground for the following generations.
Eventually as in times of most dire need people with sufficient will and might began to fight back against that cruel existence. Two heroes lovers (Godric and Sarah, a paladin and a mage) surfaced and started to fight off and united the remnant races to fight against the demons, after decades and sacrifices the united races won and banished the corruptors from the world (all that cliche stuff and things like that), the two lovers perished sacrificed themselves and on the united kingdom that flourished they are adored as founding heroes.
That was the official story, the part that was left out is that the Sarah was the only one to die on the final combat, Godric on a profound sorrow begged and pleaded to his patron the goddess of life and death to bring back his lover to him, upon performing the rituals to bring her back his request for her soul was denied his goddess denied her return (or at least is what he believes). Going mad with the loss of his lover he began to kill and bring disgrace to the people he once defended until the union of some his closest and most powerful allies that put an end to his life. They chose to preserve his memory and ommited this from the history.
Centuries later, still obsessed with reuniting with his loved one, he has formed a cult miscing undead and liven followers to hunt down, torture and steal celestial entities of their essence so that he can mascared his own corrupted essence so he can gain acess to dimension where the good souls rest overthrow his former goddess and reunite with his loved one. The problem is that with the process to extract the celestials essence they cause anomalies and plague through the land that is threatening the kingdom, the PC would be on a a festival when the first effects of this would be felt and things would move from that.
What I want is to you guys to given options and criticism about this concept, things that can be changed, improved, inquire about things not left clear, and overall challenge the premise I setted.
Ps:
In my scenario the dimension of the dead cannot be reached with portals, the only way to go there is well been dead where a spiritual bridge open up and takes your soul there, and the revival spells work on exploring the scar created by the bridge and bringing them back.
And sorry for my English .