I smell their cauldrons from here, but that's not plague they're cooking.
Pledges to the cult are forced to drink a concoction that steals their will and enslaves them forever to the Lich King.
Some say the potion contains the twisted soul of a being who was tormented before being mercilessly slaughtered, but I've never been able to reproduce it...
Fill this flask with a sample from each of the three cauldrons in the northwest region of the gate and bring it to Chief Engineer Copperclaw.
Whatdya got there, <class>?
<Copperclaw pours the content of the flask into his particle analyzer.>
Ahh... I know just the thing!