Brain Dead

Brain Dead is a murder-mystery side quest in the Fallout 4 add-on Far Harbor.

Detailed walkthrough
While roaming around Far Harbor, the Sole Survivor will be approached by a Miss Nanny named Pearl. She will then ask them if they're part of law enforcement, mentioning that there's been a terrible murder. Upon confirming, she will then ask the player character to follow her as the murder has taken place at Cliff's Edge Hotel.

Upon reaching the location she will mention that the residents have been rowdy and that she's had to get physical with some of them as they were getting too "handsy." She will then tell the Sole Survivor how the elevator is not working and thus they must take the long way around. She will then proceed to lead one through the hotel and back to an elevator, which is only to be used by the special guests. Through this path they will stumble upon several feral ghouls.

Once out of the elevator, the Sole Survivor will be prompted to speak to a Mister Handy named Maxwell through an intercom which is revealed to be vault door controls. Once done speaking they will be ushered in and escorted to the crime scene. The victim of the murder is presented as Ezra Parker, the owner of the hotel. Upon investigation of the crime scene, a bat, red paint to represent blood and the broken brain incubator will be discovered.

The Sole Survivor will then be asked by Maxwell to investigate the fellow robobrains living in the vault. The main characters that will be focused on are Julianna, Santiago and Keith, although one will eventually speak with everyone.

Questioning Juliana is rather fruitless, although talking to her husband reveals that he was a lead designer on the robobrain project, and also the one who convinced everyone to put their brains into the robot bodies. If one keeps talking to him about his research, they can eventually learn about the voice modulators which allow them to recreate their original voices.

Entering the McKinney residence will catch the couple apparently discussing the murder and a plan to run away, but it turns out they're just rehearsing lines from a script. Afterwards, Gilda will leave for the beach. Questioning Keith about the bat found at the murder scene will lead him to claim he's being framed, probably by the artist Santiago.

Speaking with Santiago gives the player character some speech checks in which they can convince him they're a fellow art lover. He will reveal that Julianna and Ezra had some huge argument in the overseer's office, but he does not know what it was about since he was trying to ignore the commotion. He will refer the player character to Gilda, the local gossip.

Gilda can be found on the vault's artificial beach behind the showers. Agree to hear one of her stories, and she'll be willing to tell the player character what Julianna and Ezra were arguing about. Apparently it was something regarding finances, and Julianna found something in the overseer's office that set her off. The argument started when Julianna accused Ezra of something, but Gilda isn't sure what.

After learning this, one will then have the objective to investigate the overseer's office, only to find it's locked. Speaking to Maxwell reveals that Ezra Parker had the key, which one can find on a desk in his room. There's not much to see in the office, but using the terminal and listening to the holotape will reveal that Ezra was embezzling funds from the vault construction fund, which is the reason the lower-class wing wasn't finished in time.

Talking with Bert, Julianna's husband, a speech check will be reveal that she's been acting very different - so much so that Bert is convinced that's not his wife. When confronted, Julianna will reveal that she is actually Ezra. Apparently Julianna discovered that Ezra had embezzled the money she gave him, and threatened to tell the others. On impulse, Ezra killed her, then moved the body downstairs, set up the crime scene and modified his voice modulator to impersonate her.

The Sole Survivor will then be given the decision to either take a bribe or continue on with the accusation which will result in a fight between Ezra and them. If the Survivor takes the bribe they can turn around and continue with the accusation, if they don't (the "let him go" option) they will then begin Brain Dead Part 2.

Once beginning Brain Dead Part 2, the Sole Survivor will be given two choices: return to Maxwell immediately and tell him about Ezra, causing the robots to attack the murderer, or wait for Ezra to leave the vault. Once he's gone, return to Maxwell and tell him Ezra is the killer. At that point, the Sole Survivor can then tell Maxwell one of three lies: Ezra got away, they killed him, or it's over. No matter which choice they make, Maxwell will pay the player character for their work.

Behind the scenes
In July 2016, the author of a Fallout: New Vegas mod called "Autumn Leaves" claimed that much of Brain Dead was copied from his mod as both share similar details. Both are murder mysteries, both take place in a vault that is ran by robots, they share many similar scenes and they have a similar interior design. The mod author, however, while believing that Bethesda did borrow much from the mod, also said they were okay with it, citing their own inspirations for their mod.

Bugs

 * Killing Ezra too quickly after the final conversation and refusing to let him go may start the quest Brain Dead Part 2 after he is already dead. In that case the player isn't able to finish the second part of the quest and the quest marker will remain over Ezra's remains. To avoid this one should wait until the second part starts before finishing him.
 * It is possible for Pearl to become stuck at the elevators, without saying the line about them being out of order. Reloading or activating the elevator in the basement will fix the issue.
 * Maxwell may not answer after activating the vault door controls. Reload before going down the elevator. Then save just outside the elevator, after killing the ghouls. Next, enter the following in the console: followed by: . Finally, save, exit, and reload. The quest should continue when the vault door controls are activated.
 * When attempting to speak to Bert or Julianna Riggs, a message may appear saying they are both busy, and thus they cannot be interacted with. Killing their cat, Scruffy, will fix this issue. Doing so will not cause them to become hostile, but it can upset the player's companions, depending who's present.