Keep in mind that an adventure which goes nowhere is no fun.
For indentifying the perp, look at what skills would seem reasonable to make such a judgement. Investigation, Contacts, Lore, etc. It's helpful to spread out the info, so that each player feels that they are involved in solving the mystery.
In the version we played, we followed the breadcrumbs...errr...clues until we found the perpetrator. For a complex game, we would have had more interference on the way to the confrontation; as it was, we only had to sneak through ghoul-held territory in following the trail.
For keeping things moving, the GM for our game emphasized a time limit; someone had been kidnapped, we had no idea why, or what was going to happen if we didn't rescue them soon.
The final battle ideas; the bad guy should be anticipating some opposition. In the chapter on running the game, there is a section on how to scale opposition for the group. Perhaps Damocles has minions/thralls trying to prevent the PCs from getting close. Keep in mind that the bad guys can concede as well; if it looks like the PCs are going to win, Damocles can flee, keeping his unlife. (Think traditional; threaten the hostage by putting them in jeopardy, then fleeing while the PCs effect a rescue.)