The Battle of Darrowshire

If you are prone to glitches (like myself) this quest is NOT as easy as it sounds at first. I read all the comments here and tried everything, doing this quest way more times than I care to admit. Learn from my mistakes.

First, placement. As you enter the town, there's a hill to your left. STAND THERE and face the town. Especially if you are at-level and/or alone, place yourself in the middle of the hill and don't move.

Second, don't be a hero. Let the NPCs do the work and don't attack anything (after all, THEY are the heroes of this battle). All the important NPCs will spawn from the well in the center of town and run down the road a little towards you. Target them, right-click on the portrait and set them as your focus. Anything they attack (this is assuming you have the target-of-target display option on), you can go ahead and attack. You can move around on the hill slightly, but do NOT run off. That way, you won't aggro any of the elite mobs that spawn down the road to your right (as you face town).

Third, pay attention. Chromie sent you there to watch the battle, so do it. Keep the hero targeted, and let them start every fight before you 'help' from the shadows. Like many others have said, LET DAVIL AGGRO HORGUS. He's not going to die in one hit, so seriously let them duke it out a bit. The one drawback of the hill position is you can't see the text they say to each other, but after doing this a ton of times and having it glitched, I just wanted this to be over, and I'm sure others feel the same.

Anyway, once Davil aggros Horgus, go ahead and finish him off. Davil will die, then Redpath spawns. Again, DON'T TOUCH ANYTHING HE HASN'T TOUCHED FIRST. Seriously. It might take a few minutes, but the beauty of this plan is the corrupted Redpath spawns literally at your feet (at the base of the hill you're on). Using the "don't touch it until they've hit it first" way I've described here is the ONLY way I have been able to complete this quest so far (since Cata) without Redpath pulling one of several disappearing acts. As soon as the corrupted Redpath spawns, NUKE HIM then run over to the well at the center of town as all the NPCs despawn. Talk to the spirit, and thank the Light you've finally completed the quest without glitches.

TL;DR -
1. Stay on top of the hill to your left as you enter town (the last hill)
2. Only attack what the MAIN quest npcs have attacked first (as long as you can do so from the hill)
3. Seriously, stay on the hill and let the NPCs fight
4. Kill the corrupted Redpath when he appears.
5. ?Spirit by the well?
6. Profit! - and tea

1. 
   
2. Go to the town square at Darrowshire (34.9, 83.9) and place your Relic Bundle.
3. 
   
4. NPC's will appear just around the outskirts of Darrowshire - help them fight the hostile mobs.
5. 
   
6. Make sure Davil Lightfire does not die (if you help him kill the mobs this shouldn't be a problem at all).
7. 
   
8. After some time Horgus will appear - kill him with the help from the NPC's.
9. 
   
10. Now protect Captain Redpath. Again, this should not be a problem with the help from the NPC's.
11. 
    
12. Redpath will eventually turn evil. Time to DESTROY him.. or just kill him even.
13. 
    
14. Hurray - you are victorious. Go to the town square and talk to Redpath. It may take some time before you can actually talk to him - be patient.
15. 
    
16. Turn the quest in at Pamela Redpath - she is in the western part of Darrowshire.
17. 
    

One note: Do NOT kill Horgus until Davil interacts with him.

I tried this again after a server restart, but because I killed Horgus when he showed up (being 80), he and Davil did not interact as intended. Eventually Davil just despawned, bugging the event.