Wild At Heart - Velen
Quest Giver: Mulbrydale Notice Board
Other Requirements: N/A
You'll pick this quest up at one of the first Notice Boards that you visit in the Velen region, I actually think it may automatically appear in your quest log when you first arrive in Velen too. For this quest you'll need to travel across much of Velen to reach Niellan the Hunter, he's over in the town of Blackbough.
Speak to Niellan to update the quest, you'll have two new objectives the first of which is to speak to the other villagers to learn more about Hanna and to venture out into the woods to check out the last place Hanna was seen. While speaking to the villagers you'll learn that Hanna did not enter the woods alone.
While you're out in the woods Margrit will approach you and offer you double Niellan's offer to stop looking for Hanna, I'd recommend you continue searching however as the reward at the end of this quest is well worth it. If you decide to accept her bribe then return to Niellan and speak with him to complete the quest. You can also choose to tell Niellan about Margrit bribing you as well to alter the ending of the quest.
After Margrit finishes bothering you, continue the search. Inspect the dog corpse that is lit up in red in the bottom portion of the area marked on your map. Right next to the dog's corpse will be Hanna's corpse, inspecting that will update the quest and Geralt will conclude we're after a werewolf.
Follow the werewolf tracks until you find them go up a tree, on the other side of the tree (shown in the screen shot above) you'll come across a tuft of fur. Inspect that to gain the werewolf's scent, now you'll see a red line through the air that jumps from tree to tree - follow it until you reach an isolated shack to the north.
Raid the shack for everything inside, you'll find a lot of tradeskill items as well as some Notes which add to the lore of this quest. When you're ready to proceed with the quest go below the shack and into the Werewolves Den. Unless it's night time then you won't actually find the Werewolf inside, you'll have to return to the surface and Meditate until night.
As for the fight against the Werewolf, they're vulnerable to Igni as well as Moon Dust, Devil's Puffball and Cursed Oil. You're going to want to defeat the wolves that come with the werewolf then focus all of your attacks onto him. It's going to be a really tough fight if you have the difficulty cranked up, otherwise it'll be pretty straight forward.
When you get the Werewolf down to 1/4th HP Margrit will come running out and beg you to stop. You can either proceed with defeating the werewolf or let him kill Margrit then take him out. Either way after the werewolf is dead loot his corpse, including the key. Return to the locked chest in the building above you and open it for the final reward to this quest.
The chest will typically include a blue item for you as well as the crafting recipe for Shiadhal's Armor.