The Lost Boy is a side quest in Valor Mortis which initiates the search for Mirek at Wolfsbane Field. Upon reaching Chapter 5, you will have to enter a secluded cave, battle with enemies, and retrieve a key from the corpse of the missing boy’s body. This guide will assist you in collecting Wounds that Heals amber and finishing the quest with ease.
Start The Lost Boy Quest

Travel the path which leads from the Wolfsbane Field lantern in Chapter 5 to the neighboring house. Make your way to the back door to find a letter left by Mirek’s parents. Reading the letter will start The Lost Boy side quest. Before making an exit, feel free to explore upstairs and find the blue memory of Mirek’s parents.
Reach the Cave and Defeat the Enemy

Set out from home along the main track and advance toward the bridge in front. Eliminate the enemies from near the house and shed, then cross the partially submerged bridge on the left. Look behind the stack of boxes to kill two more enemies before going down the path searching for the grapple point.

In case you haven’t unlocked the tree trunk shortcut to the cave, make your way across the river next to the mechanic affected by Nephtoglobin. Jump across the bridge and reach the boxes where one of the soldiers lies hidden. Finish him off and shoot the red glowing bulb to drop the tree and reveal the shortcut.
Use the grapple point to get to another level where the dangerous enemy is waiting. This enemy possesses the ability to set William on fire. You need to have a bit of distance to win the battle. After the enemy is dead, follow the way to the left and climb the slope beyond the encounter, continuing past the bushes.
Find Mirek and Collect the Cellar Key

Search for a tiny gap that you can squeeze through. It may be easy to miss, so examine the area carefully. Open the chest in the room to collect its reward, then continue toward the back and drop down to the lower platform. Inspect the deceased boy’s body and collect the Cellar Key beside him.
Unlock the Cellar and Finish the Quest

Go back to the house from where you discovered Mirek’s letter and find the door that has the Shrike symbol. Use the Cellar Key in order to unlock it and go down downstairs. Once you have entered the cellar, open the chest inside and obtain the Wounds that Heals amber. Finally, interact with the papers lying on the desk and finish The Lost Boy quest in Valor Mortis.

