Tranquility Lane

Tranquility Lane is the seventh main quest in Fallout 3, an Xbox 360/PC achievement and a PlayStation 3 trophy. The quest begins immediately after the completion of Scientific Pursuits as the Lone Wanderer sits in a Tranquility Lounger in Vault 112. The quest can also be accessed immediately after the completion of Escape! by entering Vault 112 after the Lone Wanderer leaves Vault 101.

Summary
Tranquility Lane is a virtual reality simulation housed in Vault 112, created by Dr. Stanislaus Braun. The Lone Wanderer is tasked with an escalating series of violent tasks ranging from making a child cry to killing residents. The tasks are given by a little girl named Betty, who in turn will free the Lone Wanderer's father, James, who is trapped in dog form.

As an alternative to completing the violent tasks, the player character may activate a failsafe, which will irrevocably kill everyone with the exception of Betty, James, and the Lone Wanderer. Both solutions result in the release of the Lone Wanderer and their father from the simulation.

Residents
The following are the residents that live in Tranquility Lane:

Betty's tasks
Betty will task the Lone Wanderer to do the following:
 * 1) Make Timmy cry:
 * 2) * By attacking him physically.
 * 3) * By convincing him that his parents are divorcing each other because of him, which he will believe after a Speech check.
 * 4) * By giving him the military school brochure to fool him into believing his parents are sending him away.
 * 5) * By killing one (or both) of his parents.
 * 6) Break up the Rockwells' marriage:
 * 7) * By telling Mrs. Rockwell that her husband is cheating on her, which she will believe after a Speech check.
 * 8) * By finding the lacy underwear in the Simpson household (upstairs on their bed), placing it on Roger's desk in the Rockwells' basement, then telling Mrs. Rockwell that her husband is either cheating or he is a cross-dresser.
 * 9) * By reading Mrs. Rockwell's diary upstairs, which indicates that she'd like to kill Mrs. Simpson. Take the rolling pin from the kitchen in the Rockwell house and beat Mrs. Simpson to death with it, then tell Mr. Rockwell about it. Note that reading the diary is optional. Skipping that part will not prevent completion.
 * 10) Kill Mrs. Henderson. Betty indicates that Mrs. Henderson must be murdered in a sufficiently creative manner.
 * 11) * The chandelier above the hallway to the kitchen can be rigged to drop when someone walks under it.
 * 12) * A roller skate can be moved to the stairs, resulting in Mrs. Henderson falling to her death.
 * 13) * Martha Simpson states that Mrs. Henderson loves cooking. Her oven can be sabotaged. Upon being asked to make a pie, she lights the stove and an explosion occurs, killing her.
 * 14) * The security console in the kitchen can be accessed, allowing one to enable the security lockdown, locking Mrs. Henderson in the house. Set her robot to "Begin Security Program" mode, and, as it wanders around, disable the "security parameters" data, rendering it unable to determine friend from foe. The robot will also be hostile to anyone it detects. If the robot is destroyed after it kills Mabel but before deactivating its security mode, the Lone Wanderer will not be locked in the house, deactivating the security on the terminal and will allow them to leave.
 * 15) Kill everyone: As Betty says, the Pint-Sized Slasher mask and Slasher knife can be found in the doghouse to the right of the abandoned house. At this point, everyone will become hostile and attempt to flee from the Lone Wanderer with the exception of Betty, the dog Doc, and the Mister Handy. After everyone is murdered, Braun expresses gratitude for the entertainment and tells the Lone Wanderer that Doc is actually their father, and has been watching them in horror the entire time.

Fail safe

 * 1) Old Lady Dithers will tell the Lone Wanderer that she knows that Tranquility Lane is a simulation, that Betty is really "Braun", and that he uses a "fail safe terminal." She mentions that the Lone Wanderer should go and search the abandoned house.
 * 2) Within the abandoned house, the Lone Wanderer will find a set of objects that make specific musical pitches when activated. If they enter the proper sequence, the failsafe terminal will reveal itself. In the terminal, selecting "Chinese invasion" will summon a squad of Chinese commandos who proceed to murder the residents of Tranquility Lane, with the exception of James (as Doc the dog), Betty, and the Lone Wanderer. According to the notes on the invasion program, this program disables the failsafes on the pods, meaning that dying in the simulation will kill the real-world person as well.
 * The tone sequence is Radio (F), Pitcher (C), Gnome (D), Pitcher (C), Cinder Block (B), Gnome (D), Bottle (A).
 * If one cannot remember the sequence to activate the terminal, note that each object has a specific tone, and Betty whistles the correct tonal sequence while playing in the center of the lane.
 * The solution melody is a reference to Tranquility Lane's soundtrack. The theme is played multiple times by the xylophone and once by the flute: F C D C B D A. (fail: )
 * 1) If Braun is spoken to, he will angrily scold the Lone Wanderer on what they have done and lament that he is now alone and trapped forever within the simulation, something confirmed by his own notes on the Chinese invasion plan on the failsafe terminal. The systems in place for his own safety will not allow him to be killed, even if the invasion program is launched. He will further point out that Doc the dog is actually James, and he will be waiting for the Lone Wanderer once they leave the simulation.
 * 2) Using the exit door on the playground will end the simulation.

Outside Tranquility Lane
As soon as the Tranquility Lounger pod opens, James will walk to the Lone Wanderer and begin a conversation. He had intended to find some holotapes, memos, or even experiments from Braun related to the G.E.C.K., but what he found was Braun who trapped him in Tranquility Lane as a dog. James indicates he'll be returning to Rivet City to meet with Dr. Li and resume Project Purity. This ends the quest and begins The Waters of Life. Once Tranquility Lane is exited, it cannot be accessed again.

Karma

 * Making Timmy cry will result in a -50 Karma penalty.
 * Breaking up the Rockwells' marriage will result in a -50 Karma penalty, except by killing Mrs. Simpson and blaming it on Mrs. Rockwell, which will be a -100 Karma penalty.
 * Killing Mrs. Henderson results in a -100 Karma penalty except by using the roller skate, which is a -50 Karma penalty.
 * Killing people as the Pint-Sized Slasher causes -50 Karma penalty per person or -400 Karma total for killing everyone.
 * Activating the fail-safe rewards +300 Karma.

Behind the scenes
In an August 2020 interview, Emil Pagliarulo, who worked on Tranquility Lane, and Jeff Gardiner, the lead producer at Bethesda Game Studios, both stated that they consider Tranquility Lane to be one of their favorite quests throughout the Fallout series. Gardiner cited Tranquility Lane as a good example of the dark humor in Fallout, as well as how even the most outlandish of concepts can work within the Fallout universe. Pagliarulo went on to talk about how the ratings system in the United States, specifically the limitations on killing children, influenced what could and could not occur in the Tranquility Lane simulation.

Bugs

 * Mrs. Rockwell can skip the argument with her husband if you decide to use the lacy underwear. She will just run away when she's within speaking distance of her former husband. One way to avoid this is to exit the basement before she does and make sure Mr. Rockwell is not too close to the basement door.
 * Your follower may not return to their original location upon entering the simulation, and instead disappear. Sometimes they can be found in the pod area later on.
 * If Mabel Henderson is not in her house, or leaves during the time you are arranging her creative death, she may not return. You may need to disable the security lockdown and find her, you may kill her and Betty will restore her to her house, otherwise you may have to load another save.
 * If you become hostile with one of the residents and get a fair distance away from him/her you will hear your character say "I guess it was nothing" in a child's voice.
 * When you check your watch in Tranquility Lane, the game may freeze.
 * If you start the Chinese invasion while trying to break up the Rockwells' marriage, they will survive because they can't die during that quest.
 * In very strange cases the fail-safe will not appear in the abandoned house.
 * The game may crash upon starting the fail-safe.