Chapter six starts in the city. You have to talk to the character sitting on the barrel, to receive a quest. However, on your way, you can also complete a side quest. It is a good idea to do that, if you want to earn several points.
Quest from Bolmus
Enter the house on the left. There, you will find another mouse. Bolmus will ask you to clear the basement of monsters. There, you will find fire spiders that can speed up charging of turns for the entire party and paralyze your characters. Fly to the right and avoid the traps. Do not touch the chest past the trap . Unless you are prepared for another fight.
Here, you will have to watch your step. In the chests, there are opponents. Keep flying right, across the large cobweb and you will spot a lever. Pull it, fly quickly through the traps and run through two hatches. You will have to do all that within 10 seconds, because the passage slams shut after that and you will have to repeat this action.
The blue rectangles in the screenshot mark passages that you open/shut with the lever. After you open the one at the top, the bottom one shuts automatically. After you cross the passage, you will have to fly up, avoid the trap and find a lever on the left. After you pull it, a passage will open, to a location with door to the basement. Because you have already eliminated the monsters, you can leave and talk to the character. For completing this quest, Bolmus will reward you with Magic Stardust x2.
Main story - follow up
At the beginning of the chapter, you have talked to Adolphus. Now, you have to go to Bolmus Mayor. His place is at the end of the city, on the left. As soon as you talk to him, a new party member will be waiting for you in front of the door. Robert starts with 8 skill points. You will get to the top of the rock that resembles a man's face and cross the door.
In the next location, you will have to watch out for many traps. The magma flows out from above and from below, so wait before you fly and make sure that it is safe. The majority of opponents here are fire ones, so prepare for many fights as Finn, because you are going to need water attacks.
To get to the boss and leave this location, you will have to fight 3 fights with spiders. You can find them in several spots of this location. Some of them are in the bottom-right corner of the location. There is another one a bit above the first one, and the third one is to the left of the boss arena. It is a good idea to fight him using basic attacks only. Both Robert and Rubella are good for that. They are perfect partners for Finn. Stronger attacks do not deal damage to the spiders and they only waste time. Additionally, this creates a risk that you will be attacked, while you are charging them up and lose your turn. Spiders can slow down the charging of your turn. After you have defeated all three spiders, you can start the boss fight.
After the fight, you return to the city with Robert. There, you will have a conversation after which he will decide that he wants to remain in your party. After that, you have to fly again to the rock resembling a face and talk to him, which ends chapter six.
Robert's puzzle solution
At the very bottom of the location with the boss, on the left, there is a puzzle for Robert. Toy have to match the symbols over the door with the ones on the door. You do that by using levers. The one on the right moves the two symbols on the right, whereas the other one moves two symbols on the left. The symbols that you have match have been marked in color, in the above screenshot. Grey has been used for the symbols that you have to light up. If you fail to solve the puzzle, Robert will leave the party to solve it by himself.