After grabbing the quest from the inn in Bowerstone Market, fast travel to The Drowned Farm in Wraithmarsh and follow your dog to a sneakily hidden well behind the houses here. Use the ladder to enter a small dungeon.
Work your way through the linear pathway here, killing hollow men and looting the chest that appears right in front of you (if a little to the left) as you go. When you reach the end of the area you will see Max and Sam under attack from a large group of hollow men. Kill all of the baddies and the pair will inform of a banshee attacking Bloodstone. Loot the chest sitting next to them and make your way back outside.
Return outside and head all the way back (or fast travel) to the Waterfront in Bloodstone. Make your way to the end of the large stone pier directly in front of the inn to confront the banshee.
Once you have defeated the banshee, return to Mrs Spade in the inn in (thats a lot of ins!) Bowerstone Market to complete the side-quest.