The Great Fire is a side quest of Haven playthrough in Might & Magic: Heroes Online.
The quartermaster asks the hero to find the water to extinguish the fires. The hero has to go south and pick up some water, then spout it on the six fire spots around town. Once done, the hero has to find some succubi hiding in the streets, who caused the fires. With the succubi dead, the hero has to return to the quartermaster and report what happened.