Thought Control

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

Talk to Desmond
When you talk to Desmond about Calvert (the brain that you spoke to), he tells you about his past with Professor Calvert and the Calvert family in general. He then tells you to plant a Cogwave Jammer on the Ferris Wheel that will disrupt the messages that Calvert has been trying to send throughout the Point Lookout area. Once you near the Ferris Wheel, you can hear Calvert’s voice trying to persuade you to destroy the device that Desmond gave you. There can be an error here though. When you walk up to the ferris wheel, Calvert may have not contacted you, the Cogwave Jammer can not be placed. This can be fixed by roaming the area, specifically to the item shop, and then you will be able to make the choice.

To plant or not to plant
Once you reach the ferris wheel, you have two options, but don't worry too much about them, they have no effect on karma or main storyline:

Side with Calvert

 * Destroy the jammer. Follow Calvert's instruction to place it in a nearby trash compactor. Calvert will tell you to return to the mansion, which is then destroyed in a huge explosion. There is minor loot in the Panic Room (including ammo, food and a nuka cola quantum), reached through a hatch in the center of the ruins.
 * You'll then advance to the same place as the second decision, the lighthouse, and the actual decision of who to kill is basically delayed via dialog until the very end. Also, you'll find Desmond isn't dead, but following Calvert in the lighthouse to kill him. Technically speaking this is the better karmic decision (although no actual karma is granted or removed) since you save the tribals and Desmond lives anyway.

Side with Desmond

 * Plant the jammer and activate the ferris wheel. After this is done, Calvert's voice breaks up as the jammer does its job, then a group of Tribals will attack you, and all unnamed Tribals remaining at the Cathedral will become hostile (the named Tribals will likely join them if a fight breaks out unless the unnamed tribe members are killed unobserved).
 * Return to Desmond. When you approach the Calvert Mansion, it immediately explodes. As a result of the explosion, you are knocked to the ground. Once you stand back up, walk to the middle of the house and find Desmond in his panic shelter. He begins to tell you how angry he is that his dogs were killed and that Calvert was so close to the mansion. He then states that the 200 year long feud between him and Calvert is going to end right now.

Bugs
Even after destroying the Cogwave Jammer in the trash compactor, you can still walk up to the ferris wheel and it has the "Activate Ferris Wheel" option, which if you click it it says "The Cogwave Jammer has been installed.", when it really hasn't been. (All Versions)

Reward
300 XP

Trivia
The term "Thought Control" has been around for some time, but may come from paranoia

Videos
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