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, in the Fallout 4 add-on 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 for them 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 "touchy". She will then tell the Sole Survivor how the elevator is not working and thus they must take the long way around. During this time she will lead them up through the hotel and back to an elevator only to be used by the special guests. Through this path they will stumble upon several different 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 investigating 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 you 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 you keep talking to him about his research, you 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 & 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 you some speech checks in which you can convince him you're a fellow art lover. He will reveal that Julianna & 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 you 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 you 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, you'll 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 you can find on a desk in his room. There's not much to see in the office, but using the terminal & 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 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 Pt. 2.

Once beginning Brain Dead Pt. 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, you killed him, or it's over. No matter which choice they make, Maxwell will pay you for your work.

Bugs

 * It is possible for Pearl to become stuck at the elevators, without saying the line about them being out of order. Leading her away and letting her return did not fix it - currently it seems loading is the only fix. You can also just continue wandering the hotel. Eventually when you reach the elevator in the basement and activate it the dialogue picks back up.
 * Failing to collect all three clues at the crime scene may prevent confronting Juliana, and causing the "confront Keith" option to be the only way to complete the quest.
 * The game may freeze when going into the overseer's office.