1) This quest starts at the center of Talking Island Village with Elias. He tells you to kill giant spiders and bring back poison sacs.
2) There are lots of spiders found along the west coast of Talking Island. The quest only wants 1 poison sac so just keep killing spiders until you get it. Then go back to town to Priest Yohanes in the Temple.
3) Priest Yohanes give you the medicine for Elias.
4) Elias accepts the Fever Medicine and gives you a Round Shield.