You're out with Blake to talk with the usual suspects around town, and your first stop is at a religious nut's apartment. After knocking on the door and receiving no answer, Blake will kick it down and you'll let yourselves in. You can walk around the apartment looking at all the candles, pills and crosses, but you're mainly just biding your time until Nathaniel gets home from shopping.
When he gets back, you'll start talking to him and it doesn't matter what options you pick. Eventually, Blake will jump in and drive Nathaniel to pull a gun on him with his heavy-handed tactics. At this point, you'll pull your piece out and either try to talk Nathaniel down, or blow him away. During the rest of the chapter you control, you can shoot at any time with . If you want to try resolving the situation peacefully, just keep talking. You can choose any options, and eventually you'll make it to where you can only say one thing and Nathaniel will put his gun down.
At this point Blake will begin to cuff him and you'll get a tense moment where the music ramps up, your instruction starts shaking like mad and Nathaniel turns around very quickly pulling something out from inside his jacket. It's a crucifix, so if you didn't pull the trigger, there's no harm done and Blake will continue arresting him and the chapter will end.