You will receive this quest automatically after teleporting to the swamp in [Into the Swamp].
Head to the village where and speak with one of the villagers - Aidan (M37:2). He can be found by the inn, nearby a wagon. The man won't be able to tell you anything, he'll get terrified after learning that you got to the city through the swamps. He'll tell you to head to the priest.
You will unlock [The Priest].
Received from: Aidan [Swamp] (M37:2)
Head to the temple. Once you get near, Garadel will come out to meet you (M37:3). You'll learn that the village is in danger - the monsters you came across on your way through the swamp might attack. You need to gain an amulet, which will help in casting a defensive spell. Talk with Aidan.
You will unlock [The Priest and the Amulet].
You will unlock [Aidan's Amulet].