You will learn about this quest by interacting with one of the notice boards in White Orchard. Go to the Ransacked Village and meet with Dune Vildenvert (M1,4). Dune will ask Geralt for help in searching for his brother Bastien who participated in a recent battle. Agree to help him and reach the ground where the battle took place. Explore the territory and be ready to deal with a small groups of ghouls. Look around for the fallen warriors near whom you can find a blue shield with three white flowers painted on them.
Sooner or later you will find a male corpse. After examining it, the dog will get a trail. Follow him to the forest (witcher senses will be helpful). The dog will lead you and Dune to a small cabin in which you will find wounded Bastien and a nilfgaardian deserter Rhosyn. After hearing the conversation, you have two options - you can suggest to leave Rhosyn in that place or escort him to the brother's home as a thanks for saving the life of Bastien. You will receive experience for this quest (25 points).