The Catalyst

The Catalyst is a main quest It is the final quest in the main Steel Reign questline. Completing this quest unlocks the Steel Brethren achievement/trophy.

Detailed walkthrough
Following the apprehension of Dr. Edgar Blackburn in Vault 96 and learning he was responsible for all the super mutants the Brotherhood dealt with because of his work into perfecting the Forced Evolutionary Virus, the Vault Dweller returns to Fort Atlas to find Blackburn being interrogated by Paladin Rahmani, Knight Shin, and Scribe Valdez, with Shin armed with an assault rifle. Speaking to them reveals that Shin is furious with Blackburn for what he's done, but Blackburn still admits he lives with the shame of what he's done for the betterment of humanity and that his allies will be carrying out his final plan for the FEV soon enough. Interrogating him reveals that his allies are preparing to disperse the FEV into the air and water, horrifying Valdez at how it could spread for miles, and Blackburn is willing to help stop it, though Shin believes his help is undeserving for the crimes he's committed. Asking where his allies are reveals that they are at the West Tek research center, where the FEV was first tested and created the super mutants, Grafton Monster, and snallygasters. Rahmani agrees that Blackburn's punishment can be postponed until after they deal with the FEV at West Tek. Shin prefers killing him now and razing the lab to the ground, but Valdez warns doing that could still spread the FEV, so Shin agrees to take Blackburn with them to help atone for his actions, then deal with him, with Blackburn agreeing that his punishment can wait until they can stop the spread of the FEV. Rahmani sends the Vault Dweller to West Tek to stop the release of the virus, and they will meet the player there.

Head to West Tek, and deal with any super mutants that might be guarding the facility, or slip by them using stealth to get around to the door, and head inside. If the super mutants are engaged, there is at least one super mutant suicider and two mutant hounds guarding the front door with an automated turret in a shopping cart to the right of the front entrance to the facility. The emergency exit back door is guarded by fewer super mutants, but still has one or two mutant hounds and an automated turret in a shopping cart guarding that path. More super mutants and mutant hounds await inside upon entering the Research Wing using the access code holotape if having visited West Tek earlier. Once the coast is clear, enter the elevator to the FEV Production Facility and take it down to the lab. Hellcat mercenaries under the payroll of Blackburn and his co-workers await inside, possibly a legendary one being among them. Once all four are dead, Blackburn arrives with Rahmani and Shin, both wearing their T-51 power armor, and after speaking to them about the Hellcats and grilling Blackburn about his associates, they proceed further in and find Blackburn's fellow scientists in a room sealed off by a laser grid. Dr. Farha is shocked to find Blackburn here with the Brotherhood, but refuses to be stopped from finishing their work. Speaking with her about if she is willing to release the FEV again after what happened previously with Huntersville provides a chance to use a Charisma 4+ check on her to convince her that what she is doing is wrong, but when Rahmani tries to negotiate with her, Farha makes it clear they will proceed with their plan unless Blackburn is released, and fight to ensure their plan goes through, even if it means their deaths in the process. Speaking to Blackburn reveals he has the only access code to abort the plan, so letting him go is the only way to stop the distribution of the FEV, as long as his fellow scientists are spared as well. With little choice left, he is released, despite Shin's protests, and Blackburn convinces Farha to let him in. Once inside, he asks Nellie to prepare the test chamber so he can show the Brotherhood the results of their work, despite Farha's shocked pleas. Shin is livid about this turn of events, but Rahmani realizes they've got to get in there before Blackburn goes through with being exposed to the perfected FEV.

Drop down the newly-opened hatch to the test chamber, but it is too late. Blackburn is exposed to the FEV, but something goes wrong as his fellow scientists see that something has gone haywire, and Blackburn erupts from the test chamber as a unique super mutant behemoth, with a unique club and able to launch globs of acid around the room. The player, Rahmani, and Shin are forced to engage and kill him, with his final words being "No! I was so close!". Dr. Farha and the others are horrified by what happened, and Shin reminds Rahmani that this is why the Brotherhood was tasked with securing dangerous tech so something like this could be prevented. They can't let people try playing God with things like the FEV. Rahmani agrees, but they first need to confront Farha and the others over what happened.

Using the intercom to speak to Farha, she apologizes for what happened and shuts down the production and distribution of the FEV with Blackburn's access code, but refuses to let the Brotherhood in under wanting to protect her co-workers. If unable to pass a Strength or Charisma 12+ check with Farha, the only option left is to try and bypass the locks with the nearby terminal. As an optional objective, look for the holotape that has the password on it. It will be lying on a cart across from an inaccessible security door on the far side of the test chamber from where the viewing room is. Using the password to access the terminal will allow the door to be opened, despite the lockdown from testing the FEV on Blackburn still being active, and enable Shin, Rahmani, and the player to confront Farha and her team. Farha pleads for mercy, explaining that she and her team are still valuable assets to helping humanity, despite what happened with Blackburn and the FEV. Shin wants them executed, but Rahmani wants to spare them, but Shin will have none of it, yet Rahmani believes bringing them back to Fort Atlas to be supervised by Valdez would be valuable, even admitting that Elder Maxson was right about the Brotherhood needing to secure dangerous tech to keep it out of the wrong hands, including the scientists who invented it. If the player responds with uncertainty about whether to kill Farha, Jain, and Nellie, they can speak to everyone to get their thoughts on the matter.


 * Farha, Jain, and Nellie all feel more comfortable having their lives spared and continuing their research under the watchful eyes of the Brotherhood, especially Farha as she wanted nothing to do with Blackburn's work into the FEV in the first place.
 * Paladin Rahmani also agrees that sparing the scientists' lives would prove beneficial due to the value of human lives being more important. The player can agree with her, or take Shin's side on the matter, and Rahmani will respond accordingly.
 * Knight Shin is still convinced that the scientists need to be terminated to prevent their research and knowledge from falling into the wrong hands, just as the Elders would've wanted. This allows him to finally come clean about what happened with the settlement the Brotherhood loaned the Hellstorms to, and that combined with what happened to Initiate Norland at the Uncanny Caverns only steeled his resolve to prevent people like the Raiders getting their hands on dangerous tech like the Hellstorms and killing more innocent lives with them, especially if it was because of his decisions. The player can agree with him, or take Rahmani's side, causing him to believe he's failed his duty as a knight if he was unable to sway the player to his way of how the Brotherhood should act.

After talking with everyone, speak to Farha again to make your decision.


 * (Side with Rahmani) If Farha and her team are spared, Shin is furious, believing Rahmani and the Vault Dweller will only repeat the mistakes of the past. Despite Rahmani's attempts to talk him down, Shin has every intention of returning to New California to report Rahmani's actions to the elders in person. The player can either try to talk him down, or attack him. If attacking him is not chosen, he and Rahmani will exchange some final, bitter words before he takes his leave to head back, collect his initiates, and depart to return to Mariposa and Lost Hills to tell Maxson and the other Elders of Rahmani's actions.
 * (Side with Shin) If Farha and her team are executed, Rahmani is disappointed that she could not sway Shin or the Vault Dweller to her way of thinking with the Brotherhood and away from that of the elders and loyalty to them. As a result, Rahmani can either be killed or spared depending on the player's decision in conversation. If she is not killed, she leaves before Shin and the Vault Dweller execute Farha, Jain, and Nellie, not wanting to witness the cold-blooded murdering of the scientists after exchanging some final bitter words with Shin after he brands her a traitor and she decides to rebuild the Brotherhood to her way of thinking elsewhere. Shin decides that Rahmani is no longer a member of the Brotherhood and exiles her, stripping her of her title as paladin, leaving him as the highest-ranking member with his position as Knight to take over leadership of the Appalachian Brotherhood.

After the decision about Farha and her team is made and the fallout between Shin and Rahmani is dealt with, return to Fort Atlas for a final debrief.


 * (Sided with Rahmani) Returning to the fort, Rahmani, Valdez, Initiate Ramirez, Russell, Max, Initiate Hewsen, and if they were spared or convinced to return to Fort Atlas, Marcia, Farha, Jain, and Nellie, and either Colin or Marty Putnam, will be waiting with the remaining initiates to congratulate the player for their efforts with helping the Brotherhood. After Rahmani explains what happened to Shin, either having killed him or explained that he has departed to return to New California, having put his loyalty to the Elders above slandering the Brotherhood's name, causing murmurs among the initiates, Rahmani invites the player to stand next to her and Valdez as she dubs them "Knight-Errant", to cheers from the initiates.
 * (Sided with Shin) Returning to the fort, Shin, Valdez, Ramirez, Russell, Max, Hewsen, and depending on earlier choices, Marcia, and either Colin or Marty Putnam, will be waiting with the remaining initiates to congratulate the player for their efforts with helping the Brotherhood. After Shin explains that Rahmani has been exiled from the Brotherhood because of her actions with defying the Elders and her bleeding heart, or been killed, but not without some remorse in doing so, he invites the player to stand with him and Valdez to be given their new title of "Knight-Errant" with the Brotherhood.

After the debrief, speak to Valdez, Hewsen, and Russell as optional objectives regarding what's happened, and after that, speak to the remaining commander of the Brotherhood, depending on if the player sided with Rahmani or Shin, and after exchanging some final words with them, the final quest of Steel Reign is completed, unlocking the corresponding achievement/trophy if it was the first time completing it, along with caps, XP, and other random rewards. The ability to craft Hellcat power armor is also unlocked upon completing the quest.

Rewards

 * ??? Caps
 * ??? XP
 * Power armor chassis with full set of Hellcat power armor

Behind the scenes
The Blackburn boss fight at the end of The Catalyst was primarily designed by Joshua Moretto.