|The following is based on information from Fallout: Brotherhood of Steel.|
The Initiate enters the town of Carbon based on information that the Brotherhood of Steel is on a mission in this area. Eventually, they will learn that the Brotherhood of Steel Paladins moved on to the town of Los in pursuit of the super mutant army lead by Attis, and technology hidden in a Secret Vault. In Los the Initiate will find that the Brotherhood Paladins did not survive, and the only surviving member Rhombus is in need of help.
Asking around town leads to little information, until the Initiate talks to Richard, the mayor of Carbon. Richard claims to know the whereabouts of the Brotherhood of Steel Paladins and tasks the Initiate to clear the radscorpions from the Carbon warehouse before he will provide the information. As the Initiate is dependent on others to go anywhere in the game, they need to complete this task.
After a task to gain the Mayor's trust, Richard informs the Initiate that the Paladins went into the Carbon Crater, and gives them an elevator key to go in after them. The Initiate must then search the crater for the Brotherhood, a futile quest, as once they reach the bottom of the crater, they find that they got lured into a trap.
Running out of leads the Initiate eventually heads to the Carbon Mill. After witnessing the confrontation between Jane and Attis, the Initiate will be spotted by Jane, who then challenges them about killing her soldiers. During the questioning, she claims to work for the Brotherhood of Steel, saying that she is offering information on Attis' army in exchange for protection, and the Brotherhood turning a blind eye when it comes to her dealings with the townspeople and the mutants. She mentions that. after her meeting with the Brotherhood, they went on to pursue the mutants in a ghoul city.
Once the Initiate travels to Los, they follow the lead from Jane that the Brotherhood are seeking out the super mutants to defeat them. They search Los for the Brotherhood Paladins, but finds only Rhombus still alive.