Captured by Mind Flayers

Eastern Caverns in Underdark; 285000 ex.
 * Captured by Mind Flayers
 * Enter the Eastern Caverns in the southeast corner of the Underdark and you will be captured by Mind Flayers and thrown in a cell.
 * After a little while, an ogre will appear and explain the situation to you. He will then lead you to the Gladitorial Fighting Pit and you will have to fight three Umber Hulks.
 * When you are returned to your cell, open the door to the northeast and speak to Simyaz, leader of the Githyanki, who have also been captured by the Mind Flayers.
 * The Githyanki will leave to fight and when they return, Simyaz will ask that you aid them in their plan to escape.
 * After a little while, the ogre will appear again and both you and the Githyanki will appear in the ring together.
 * While the Githyanki are keeping the Mind Flayers at bay, attack the Kuo-Toa and leave out of the door to the east.
 * 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 larget machine in the northeast corner of the room four times to get four Control Circlets.
 * 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 will attack you.
 * The Githyanki will appear and thank you for allowing them to get free. They will leave you behind, however, so you will have to fight your way out yourself.
 * 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 west most passage and to the north, you will find another door that can only be opened by a Mind Flayer. 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 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.