In the druid settlement you can find an alchemy master - Gremist (M13,9). You can start this quest to receive some alchemy ingredients and the possibility to trade with him. However, the druid isn't eager to teaching so you must do three things for him (in any order you want).
You must obtain alcohol from the old distillery on the hill. Entrance up can be found on the northern side (the path at the slope). At the top of the mountain you will have to kill three aghouls (level 26). When you enter the distillery you will find an cyclops there (level 21). Take care of him (it is wise to use large amounts of fire), then search for notes in a wooden shed. After reading it search for a mash. It can be found on the scaffolding near the containers on which you can climb via the ladder.
Then place it in the tank and then burn the fire under it. When Geralt will say that you can freeze the drink, use the lever by switching first the right, then the left. After another comment the drink will be ready to take from the barrel nearby.
Find Fritjof in the Blandare village. He will agree to help you if you will help him first. You must protect him from monsters while he will perform a ritual.
Your enemies will be muckixers (level 23) attacking in pairs. If you don't manage too well in the battle against them, simply try to draw their attention. Lightning bolts appearing from time to time and druig's dog will be very helpful. After all is done, Frithof will go to the place where the ritual takes place, to druid.
Then go to the forest in order to find a rare plant - the pimpernel. At the destination you will only find leaves, with no flowers. Some druid will start a conversation with you and will accompany you in your search for the person that responsible for the fact that you can't find the flowers.
Not far further you will find a succubus - she is responsible for taking the plant. If you want to, you can kill her and obtain the ingredients and mutagens. In that case you will have to keep going down the path to the cave in which the succubus lived, you will find the pimpernel there. However, if you spare her life, you will simply avoid the battle - you will be guided to the same cave from which you will be able to take the plant you seek.
Important - if the druid doesn't appear, you can go directly to the cave - South from the place where you will find the herbal, there's a path that will lead you to the succubus cave, where you can collect the pimpernel.
After you complete all preparation tasks, you can go back to the druid in order to start the "ritual". After bringing all the ingredients to the druid he will tell you to leave his house and go back the next day. Do as he says and talk to him. The quest will end and you will receive few rare alchemy ingredients as a reward. Additionally, you will be able to trade with the alchemist. He has many runes and valuable alchemy ingredients.