Kill in Stormhold until a mob drops Sword of Thunder (Note: Sword of Thunder is tradeable and may be found on the broker.)
NOTE: Do NOT accept the quest until you complete the dialog. If you do, the quest may become bugged. At the end of the dialog a new item will be put in your inventory called "Berik, Sword of Thunder" Examine this Sword and accept quest. This is the sword you will need to inspect after each further step.
IMPORTANT: As of 12/07, you can get this sword by killing random mobs in Stormhold at ANY level. Even if the mobs are grey, the chest will drop since it is a quest starter - not loot. It is a random drop throughout the zone, albeit somewhat rare.
Examine the Sword of Thunder.
Berik, Sword of Thunder will tell you to kill 100 undead knights in stormhold. Only undead count. All skeletons and zombies work (Knight, sentry, squire, defender, burnt, etc.) Once this step is done talk to the sword again.
Next it will ask you to kill 3 named bosses in Stormhold: