So I've got an interesting story I'd like to try and play out with Black Crusade.
The story starts with a daemon prince of Tzeentch, known as Khaliman, fighting against a captain of the Raven Guard, known as Randolphus. Randolphus is victorious and Khaliman is shattered into hundreds of pieces and strewn about the warp. Randolphus is later dreadnoughted due to wounds incurred in that battle.
Jump ahead 500 years and Randolphus has been made first chapter master of a fairly new chapter of space marines, The Emperor's Nightmares. It will still be thousands of years before Khaliman reforms on his own, so the remains of the minions of Khaliman, led by the players , plot their revenge upon the chapter and Randolphus.
The idea is an Ocean's Eleven style heist where they would steal the soul of Randolphus out from under the chapter. Maybe even use it in some ritual to aid in Khaliman's return. Yes, this is intended as a fairly high level Black Crusade campaign, seeing as the party would be up against an entire chapter of space marines.
How might the players go about doing this? I have an idea for an artifact of Khaliman that would allow them to astrally project, at the cost of severe levels of corruption
What sort of other resources might the players need? Does this even seem viable?