- Enter the Mind Flayer Dungeon from the southeast corner of the Underdark. The Mind Flayers will use their magic to make all party members unconscious. After becoming conscious again, you will find out that your party is locked up in a cell and that you are prisoners of the Mind Flayers.
- After a some time, an ogre will appear and he will explain that you must fight creatures to entertain the Mind Flayers. He will then lead you to the Fighting Pit and you will have to defeat three Umber Hulks.
- When you return after surviving your first battle, open the door to the cell northeast and speak to Simyaz, leader of the Githyanki, who have also been captured by the Illithids.
- The Githyanki will leave to fight a round in the pit and when they return, Simyaz will ask that you aid them in their plan to escape.
- After a little while, the ogre jailer will appear again and both you and the Githyanki will appear in the ring together.
- While the Githyanki are keeping the Mind Flayers occupied, attack the Kuo-Toa and leave out of the door to the east.
Tip: you will fight a lot of Mind Flayers before you escape, who can kill any party member by draining intelligence to zero in two or more successful hits, depending on the intelligence of the character. The rage abilities from Barbarians and Berserkers will give one party member protection from mind effects, who then can tank for the party. Also, if you have Clerics or Druids in your party, they can cast the spell Chaotic Commands upon themselves or a party member, which also provides protection from a lot of mind effects. There is nothing which can protect you from intelligence drain.
- Go to the east end of the area and click on a blood vat to get some Illithid Serum.
- Use the Illithid Serum on one of the machines in the southeast corner of the area to free the slaves.
- Click on the large machine in the northeast corner of the room four times to obtain Control Circlets, four in total. If you should run out of Control Circlets, you can also transform into the Slayer to open the doors, as the Slayer is an immortal being.
- Return to the room with the blood vats and use one of the Control Circlets on the Mind Flayer to take control of it.
- Go to the room to the north and move the Mind Flayer to one of the doors. Both of the doors will open and the Mind Flayer which was under your control, will attack you.
- The Githyanki will appear and thank you for helping them escape. They will, however, leave your party behind, so you have to find your way out. You can find them somewhere in the Underdark, if you would like to pay them another visit.
- Enter the passage to the west and then go north. Collect Brine Potions from each of the birthing pods. These potions will grant you temporary immunity to the Mind Flayers' psionic attacks.
- Defeat the mind flayers in the southwest room. This will be an extremely difficult battle. To the north, you will find another door that can only be opened by a Mind Flayer or an immortal being. Use another Control Circlet to take over another Mind Flayer (if you can't find one, another should appear in the east-most room with the blood vats) and open the door.
- Behind the next door is the Master Brain. Once you have defeated it you will receive the Elder Brain Blood. There are quite a few valuable gems left by the Master Brain's body.
- Go to the exit and the Slave Leader will thank you again before all the slaves leave through the exit. Follow them out of the Mind Flayer lair. These slaves are followers of Ilmater, and they promise you a reward, if you can find them again when on the surface. You can probably find them again in a temple of Ilmater or a tavern.
You can find some unique equipment here. Near your cell, you can find the hilt of The Equalizer.
A Ring of Fire Control can be found as loot when opening the strange things southwest of the area. The crazy dwarf drops it when he is killed.
Harp of Discord is hidden in the wall near the door to the entrance.