After completing La Cage au Fou, you will watch a flashback of Count de la Croix and Dettlaff's first meeting and their last, where the higher vampire seemed grief-stricken to kill his friend. While there's no objective marker or indication that there's a secret quest at the crime scene, there actually is! However, if you don't complete Amidst the Mill's Grist in The Witcher 3: Blood and Wine straight after La Cage au Fou (and before Where Children Toil, Toys Waste Away), then you will miss it forever, unless you start another playthrough.
Amidst the Mill's Grist starts when you reach Count de la Croix's Mill, which is just a short walk south-east of Corvo Bianco Vineyard, as marked on the map above. This quest will only activate once you arrive and kill the bandits, but it will only activate after La Cage au Fou and before Where Children Toil, Toys Waste Away.
The mission is extremely straightforward. You kill the bandits, enter the mill, investigate the footprints to get the Mill for Sale note, and examine the blood stains on the top floor. While this mission is extremely simple, it's one that most of you might have missed without a guide, since there's no indication it exists, and proceeding with the next main quest will cancel this quest.
For your troubles, you will be awarded 400 XP, which is pretty generous when all you have to do is kill some bandits and look at a bloodstain. While this is a secret quest, there's no real reward from completing it, and there's no secret outcome that will turn the tides of the main story for Blood and Wine; it's just a fun secret to discover after La Cage au Fou.
سەرچاوەی فەرمی بە زمانی ئینگلیزی: https://gamerant.com/witcher-3-amidst-mill-grist-walkthrough/
