Blind Betrayal

Blind Betrayal is a Brotherhood of Steel main quest and achievement/trophy in Fallout 4.

Background
As the Brotherhood of Steel finds itself on the verge of success in their Commonwealth invasion, a startling discovery is made of one of their own. A paladin that was considered one of their best, has a secret, and now a hard decision needs to made for their future.

Detailed walkthrough
After Liberty Reprimed is completed the Sole Survivor is ordered to report to the Prydwen. There, a furious Elder Maxson confronts the Sole Survivor, demanding to know if they were aware Paladin Danse was a synth. He reveals that the network hack of the Institute's mainframe yielded indisputable proof Danse is not human, but is actually a missing synth unit with the designation M7-97. The Sole Survivor is then given a choice of medium-difficulty persuasion checks to convince Maxson they did not know Danse's true nature. Alternatively they can suggest that Danse himself may not have known he was a synth.

The Sole Survivor is then ordered to find Danse, who has gone AWOL, and execute him. They meet with Proctor Quinlan to figure out a way to track Danse down, but their deliberations are interrupted by Scribe Haylen. Haylen pulls the Survivor aside and makes a plea for mercy on Danse's behalf, desperate to save him even if he is a synth. She then directs the Sole Survivor to the recon team's previously declared fallback location: Listening Post Bravo.

After dispatching the security measures (two exterior turrets, one exterior Protectron, and three additional Protectrons down the elevator), the Sole Survivor will locate Danse inside the bunker. There they must decide how to proceed.

Plan A: Carry Out the Execution
The Survivor may execute Danse with or without speaking to him. Alternatively one can let him commit suicide. On his body they will find a synth component and Danse's holotags. Collect the tags, return to the Prydwen, and inform Elder Maxson the deed is done.

If the Sole Survivor enters the bunker and is seen by Danse, then leaves the bunker, Danse will commit suicide.

Plan B: Allow Danse to Live
The Sole Survivor may refuse to execute Danse. He will protest, stating synths are abominations and that he must be made an example of. Passing a medium-level persuasion check will convince him he is no threat to humanity and should flee the Commonwealth. Danse hands over his holotags to appease Maxson, then asks the Sole Survivor to meet him on the surface to say their farewells.

Outside the bunker Danse and the Sole Survivor are met with an unwelcome surprise: Elder Maxson, having suspected the Sole Survivor would prove insubordinate, has followed them to the bunker. Outraged, he reiterates his orders and demands the synth's death. From here the Survivor has three options:
 * Concede to Maxson and kill Danse. Danse will submit peacefully.
 * Fail to convince Maxson to spare Danse OR request he perform the execution himself. Maxson will kill Danse.
 * Persuade Maxson to let Danse live. Maxson will reluctantly agree, but will exile Danse from the Brotherhood. As a known synth Danse will be fired upon by Brotherhood soldiers.

Whatever decision is made, return to the Prydwen. Maxson will promote the Sole Survivor to the rank of paladin in addition to granting them all of Paladin Danse's belongings, including his living quarters (the room marked "Prydwen Quarters" which is locked before this quest) and his personal set of T-60d power armor.

Bugs
Blinder Verrat Ślepa zdrada Traição Cega Слепое предательство Сліпа зрада 盲目的背叛