Talk with Count Borhis di Salvaress at the Trading Post in the north of Toussaint and search for clues in the area. This will expand the quest and give you a choice of whether to kill the monster or not. In this case I decide to team up with the Crinfrid Reavers and dispatch the beast. Whether you do or not doesn’t have any real bearing on the game, but it is at least an interesting dilemma.
Video: Mutual of Beauclair’s Wild Kingdom
The Witcher 3 Guide 