Sage Highmesa, standing just south of The Dens of Dying, has asked you to use Highmesa's Cleansing Seeds at a Den of Dying Plague Cauldron to neutralize it.
I'm convinced that the plague is being caused by something in the caves up there.
<Class>, I want you to take these seeds. I normally use them as a ward against the Scourge, though perhaps they can be used to disrupt whatever foulness is happening in the dens.
Find the source of the plague and throw them into it.