After giving Commander Elsurion the package to complete A Long Journey, talk to him again and he will tell you about a gang of marauders who have been plundering the area. You agree to help.
Your first stop will be Skook's Corner. On the river there, you will find a fisherman named Arduval. He will tell you that the marauders have moved on and suggests that you go talk another fisherman.
This second fisherman is Meltinir and you will find him on the river (fishing, of course) near the Wargfels portal. Again you are too late. He will direct you north along the river.
In West-Skookemchuck, you finally catch up with the marauders in their camp. There are quite a few of them, but it should not be a difficult fight.
After defeating the marauders, return to Commander Elsurion for your reward.