At Lighthaven fountain search for an NPC called Vincent Swiftblade. Talk to him and he will say that he needs a group of heroes to make a coordinated assault on three different camps. Say “Olin Haad”, “Tarnian Wolfmane”, “Yes”, “Details” and he will give you more details of your task.Head to the Lighthaven west bridge. Go through and then head north. You will end up at their 1st camp. It's easy to locate the camps, just search for the catapults. Kill 15 Mercenaries until the Mercenary Lieutenant spawns. Kill him and move to the next camp. The 2nd camp is located just northeast of the 1st camp. Kill again 15 Mercenaries and then kill the Mercenary Lieutenant. Head east and follow the path until you reach the 3rd camp. Once again kill 15 Mercenaries in order to spawn the Mercenary Lieutenant. Kill him and you will get the following message

As the mercenary lieutenant falls lifeless, you hear a loud war call from the northern camp.Follow the path east (turns west) until it ends. Continue walking west and you will end up at some abandoned houses. Find Mercenary Leader and kill him. Head back to Vincent Swiftblade.

Talk to him saying “Reward” and you will be rewarded with 750*lvl exp points and 500 gold pieces.