This page of A Plague Tale Innocence has a walkthrough for chapter 7 - The Path Before Us. It focuses on the siblings journey to the alchemists' castle. Read the walkthrough to, e.g. learn how to follow Melie, how to escape from the hideout during the night, where to find the castle, or how to get rid off the rats from the castle's yard.
The whole thing begins with you following your friend. Soon, you will arrive at the mill. The entrance is locked, but it's not a problem, as Melie can quickly deal with the lock.
In the mill, you will find a curiosity. To move on, you have to solve it. Getting to the other side requires stopping the mill. Go to the wooden wheel on the left . Turn them to slow down the movement of the mill. Then tell Hugo to pull the lever located on the opposite side of the platform .
Thanks to this, the mill will stop, and Melie will be able to go to the other side. Tell her to turn the wheel, located in the center, right in front of you . Then let Hugo move to the other side and pull the lever there . So also you will be able to go to the other side.
Once you're done, follow Melie again. When passing through the abandoned village, Hugo will have another attack, and you will have to carry him. It won't last long. You'll be at the shelter in a minute.
Escape from the hideout
Unfortunately, you will be forced to flee the asylum. The emergency exit leads through a narrow tunnel. As it turns out, it's also guarded. At the first opponent, Melie will teach you how to create the Devorantis. This type of projectile allows you to burn through steel. This forces enemies to take off their helmets. Which, in turn, makes them vulnerable to ordinary stones. This is the way you will be able to eliminate the enemy in the tunnels.
After getting out to the open, you will get into the woods. There you will meet with strong resistance. Due to the limited possibilities of distraction opponents, you have to eliminate them. For enemies without helmets, use ordinary stones. If they wear helmets, you should first treat them with a Devorantis. Remember to always be hidden in tall grass.
At some point, you will encounter a large cluster of enemies. In this case, you have no way to distract them. Worse, if you warn just one of them, it will automatically trigger the others. Therefore, you must be absolutely sure that your actions are clandestine. A mistake will cost your life. Shoot from tall grass, and only in opponents who are close to others.
At the end of the area, you'll see a gate. It is locked, but Melie will open the side passage. Once you pass through the structure, you will meet a soldier escorting Lucas. Free your friend using a Devorantis and an ordinary stone.
Looking for the castle
Then the three of you will proceed. You'll only find a small group of rats that have focused on the alchemist's cart. At this point, you will learn the recipe for Luminose. It's a kind of explosive. It's useful against swarms of rats.
Follow the path until you find yourself on a raised ladder. Shoot down the chain that holds it. It'll let you go upstairs.
So you will get to the cave with the lake. Use the boat to get to the other side. Tell Melie and Lucas to bring it with the wheel on the shore.
Then come with Hugo in the boat and swim to the other side. Once you're there, pull the wheel to bring the wheel to Melie and Lucas so that can get across.
Go through the door. You are trapped in a corridor full of rats. Light the hearth, go to the elevated part on the right. There, you will find a lever that controls the hearth. Slide them all the way forward. Then jump down with Melie and go to the second elevated place.
Come to the drawbridge. Lower it. You will be taken to the shelf where you started, however, on the other side of the gate. Melie will take care of the lock. Light another hearth, and then move it to the center of the room. Thus, you will reach the goal of the journey.
Follow the stone shelf. At some point, you will reach a fragment captured by rats. Use a flash of lightning to run.
Then, you click another such fragment. This time, it's bigger. You will need to use a sheaf of hay. Light it when you get to it. Wait until the next lightning bolt and move on.
Clearing the castle's yard
Then we got to the courtyard of the castle. Light the nearest hearth and move it to the stairs. Also set fire to the next hearth. Then take a stick and set it on fire. So that you get to the stairs.
On its top, you will find a mechanism. Turn it all the way to the end. This will remove the rats and allow Melie to pass. Then, lower the bridge.
Go to the next mechanism. Light the fire and come down. Tell Melie to move the mechanism. Follow the light. Then light another hearth and climb the shelf. There, drive the car to the end.
Wait until the mechanism released by Melie will pass you, and go back to the initial location. Your friend will be waiting there. Climb to another mechanism. Lower the bridge and return to it. Light another movable hearth and go down to the light source. Follow him to the next hearth.
Light it and take a stick. You will use it to get to the ladder. Set the torch on fire to reach that place. Move the hearth. Melie will release the mechanism and make the rats run.
Lastly, move the exterior mechanism - the one you have moved earlier. It'll push all the rats into the moat.