welcome,
The quick summary of this plot is that a creature - most likely a corrupt angel - will try to summon Lucifer, the first 'guardian of death'. A bunch of people will go missing - some may die, some may live. For the summoning, there will be plenty of blood given from rare creatures and mixrs, like a mix between werewolf and vamp or anything that really shouldn't exist because of enemy lines or 'natural' reasons. At least three missing people have the chance to die because they will be put close to death as offerings to Lucifer. If Lucifer likes them, they will live as his slaves. If he doesn't, then they are dead.