The main goal of this side quest is to investigate the cause of death of a man found near a property. Exploration of the villa will lead to some astonishing revelations and will force Geralt to eliminate living statues. Note - don't start this quest when you're below the required level (an absolute minimum is level 40), as the final battle of the quest will be extremely difficult.
Unlocking the quest
This quest can be unlocked by approaching a property located to the east of the Francollarts village, in the southern part of the kingdom (M5,7). Here Geralt can meet with Gaston, a merchant kneeling next to a corpse. Initiate the conversation and examine the corpse. Geralt will decide to investigate the cause of death of the man.
Examining the property
You can explore the properly on your own, or take Gaston with you. The second option is the better one, as this way the life of the merchant won't be threatened. Head towards the property and use Witcher Senses along the way. Examine the blood stains and use the Aard sign on the closed door. After entering the property investigate the flipped table and the corpses located in the area. Finally, check the ceremonial bowls lying next to the throne and the burnt mark located on the left side.
Head upstairs and remember to examine subsequent bodies. Your destination is the door located on the upper floor of the property. Knocking on the door will allow Geralt to meet with the owner of the property, Durand.
Replaying the scene
Durand will give you a Ceremonial Mask. Reach each one of the lamps and press the interaction key/button to light them. Pick up the Elven bread from the chest and place it on the bowl on the left side. Get back to the chest, pick up the Elven wine and place it on the bowl on the right side.
Open the chest once more. Pick up the Ancient elven sword and Ancient elven shield from it. Geralt must be using both of those items. Open the inventory and place the items in the slots shown on the above screenshot - the elven sword must replace Geralt's steel sword, whereas the shield must be placed in the pocket. Select the shield from the drop-down menu so that Geralt can start using it. Finally, stand in front of the throne and kneel.
Defeating the Living Statues
At the end of this quest awaits a difficult encounter with Living Statues. At the beginning of the fight set the Quen sign as your active one - this will protect Geralt from the elven attacks. Additionally, the protagonist can use the shield to block attacks. Focus your attention on the living statues of elven women, as both of use magic and can make the whole encounter a lot more difficult. When they are dead get rid of the remaining statues of men - you can now use your favorite quick or slow attacks of Geralt.
After the encounter ends speak with Durand and Gaston again. You will be given 300 crows and experience points.