Setting: swords and sorcery
Theme: straight-up good old-fashioned Good vs Evil
Synopsis: an Evil demon lord and his Evil minions once tried to take over the kingdom, but they were defeated by the forces of Good. However, one of the demon lord's more loyal demon minions made preparations to bring the demon lord back for another shot much later. These preparations involved, among other things, a very specific human sacrifice of a specific girl. However, the forces of Good arranged things so that the girl would be hidden and protected. But the forces of Evil are out looking for the girl, and if they locate her they will stop at nothing to get her.
Eventually I have this big battle planned between the demon lord and his minions (lesser demons, evil monsters, etc) and the good guys, the demon's last ditch effort to get the girl and the good guys last line of defense to protect her.
The problem I have is, how to bridge the gap between. I would like to reveal bit by bit what the demon lord is up to, what girl he needs to return to full mortal-stomping power, and why. I would also like to reveal to the PCs how the forces of (supernatural) good (angels, archons, whatever) were also at work trying to protect the girl and thwart the demon lord. I have the idea that no one- not even the girl herself- knows how important she is except said forces of good (the fewer who know, the better). So there's kind of a double thread of exposition here.
I think what would help me now is some ideas of how to provide exposition bit by bit. I've been brainstorming adventure hooks that could help push things along, but I'm rapidly running out of ideas- and the ideas I have so far I am not crazy about. Help!