Breathe Deep
The next quest line you have will consist of you going into the Bog of Souls which is a very dangerous and toxic place. He tells you that a woman named Gia can give you a brew to let you survive in the Bog of Souls.
Head on over to the location to speak with Gia.
Speak to Gia to tell her about your current predicament. Tell her that Zarek sent you to have her cooperate.