A Meeting of the Minds

 is a Fallout 3 quest and achievement that is added to the game with the Point Lookout add-on.

Walkthrough
When you talk to Desmond he tells you about Calvert (the brain that you spoke to) and why they have been fighting for centuries. He then tells you to plant a device in the Ferris wheel that will disrupt the messages that Calvert has been trying to send out. Once you near the Ferriswheel, you can hear Calvert’s voice trying to persuade you to destroy the device that Desmond gave you. Destroy it, and Calvert gives you a little present called death. Well that’s what he calls it, but whether or not it actually happens depends on you. He will send a bunch of robots out to kill you and you decide whether or not you die. If you chose not to destroy it and instead plant it on the Ferriswheel, you will immediately be attack by Tribals who come at you from the ground and are sniping at you from the rooftops. Kill them and then make your way to the Mansion. When you try to approach it, it immediately explodes and parts of the house go flying everywhere as you knocked down to the ground. Once you stand back up, walk to the middle of the house and find Desmond in his little safety cellar. He begins to tell you how pissed he is that Calvert killed his dogs and that this fued between them is going to end right now. Tell him you are ready to go and you will both make your way to the Lighthouse. Once there, enter the Lighthouse when you are ready. When you enter, a sliding plate at the bottom of the Lighthouse slides away and reveals a door to what is called the “Underground Lab”. In the lab, you will make your way to a room with a closed metal door. Kill the turrets that begin to attack you and make your way through the hallway behind the closed door. As you make your way through the hallways, look in the rooms and get supplies that are in the ammo boxes. When you get a good ways down, your character starts to have moments were the screen goes fuzzy like when drug effects wear off. When you find the brain you must talk to him and decide what you’re going to do. You can either kill Desmond, which can result in death, or you can kill Calvert in which you get to look the room behind him. To kill Calvert you must be quick because he sends his Protectrons out to kill you. It takes a couple of shots but eventually the glass will break and the brain will be no more. Then talk to Desmond and you are finished. Go to the door in the information room and inside you will find a workbench covered with lots of Energy ammo, a Microwave Emmiter, two ammo boxes, and a safe with some money and other random stuff in it.

Reward
If you do, the Professor will reward you with the best thing any human could ever hope for...death.

Or at least he'll try, he will send the robots (difficulty will dictate which type robots they are) kill them and loot Desmond's body and find his unique glasses (5 points to small guns and explosives).

If you don't want to kill Desmond, shoot the brain until the glass shatters and the water completely drains and then shoot the brain itself. After the brain is dead talk to Desmond, he will give you a key which unlocks the door which requires a key nearby. Inside this door is a lot of ammo for energy weapons and weapon components as well as the Micro-Wave Emitter. And if you feel like being dirty and don't really care about Desmond, you can kill him afterwards and claim his Eyeglasses which have a plus 5 to Explosives and Small Guns. He also carries a Combat Shotgun and a Sniper Rifle.