There's really only one tricky bit with this quest, and it's at the fountain in Moonbrook. Assuming no one else has cleared the area for you you'll see a mob at the cart and a mage at the fountain. Because the traitor won't stop unless he's engaged in combat, the first mob aggros and runs after him but doesn't stop him until he's in aggro range of the fountain mage. As soon as the mage hits the traitor, he runs to the fountain and aggros another mage on the other side. Be ready with poly, sap, a pet, or a friend to stem the tide.

Note that this portion of the quest isn't given by Stoutmantle, but rather by The Defias Traitor at the bottom of the tower steps. It took me forever to figure that out.

Soloing this as a 15 Priest was not an issue. This quest is a lot easier to solo now that escort NPCs are not quite as pants-on-head retarded as they once were.

In ye olden days of yore, if enemies aggroed you, the escortee would gleefully disregard your plight and keep walking while you were trying to keep yourself alive. Typically said escortee would then pull the next four mobs onto himself while you're still fighting the first one, die in roughly two seconds, and then you'd tend to join him shortly after. But in this modern, glorious age, the escort AI will now stop and assist when you are attacked. Apparently Blizzard decided that the hunter/warlock pet defensive AI might be useful for these NPCs. Knowing this mechanic, you can do some preemptive pulls and avoid getting shoved into a 6-on-2 fight. Just note that merely aggroing something will not switch the escort to attack mode -- you must take damage before the AI switches from walking to assisting.

Also, the Defias Traitor can be healed and buffed with any means you may have, so https://vanillawowdb.com/?spell=1244 charge him up before you step into Moonbrook.

Lastly, recent patches have added a graveyard just northwest of Moonbrook. Keep the Traitor up at all costs, draw aggro off of him and sacrifice yourself if necessary. If you should die, he can hold his own against a single mob for a few moments. Just run back, res, and rejoin the battle as quickly as you can. As long as he doesn't die, you won't fail the quest.