What brings it on is Quinn, although it's not completely his fault. And in a way not his fault at all. It's whoever's been spying on Carrie from across the street - that got Quinn into his professionally defensive frame of mind. And it's the media, surrounding Carrie's apartment, and bombarding Quinn at the door with questions. And the police only made things worse.
Given Trump's know-nothing and dangerous attacks on the press from his literally bully pulpit, I don't like to see the media portrayed this way, though I suppose there's a least a little truth in local cameras congregating around some subject's house at a time like this.
On the other hand, had New York really been subject to a bomb attack on the bridge - which fortunately only killed two people - the media would likely have had more important things to do than form a mob in front of Carrie's house.
Quinn was right to shove the lady reporter out of Carrie's house, but wrong to shove her down the stairs. He was completely right, however, to shoot and wound that jerk who threw a rock in Carrie's window, which could have killed or badly hurt somebody, including Carrie's daughter (who again had some of the best lines of the evening).
And the police gave a poor accounting for themselves. Whoever was in charge should have listened to Carrie, sooner, and a lot of what happened could have been avoided.
All of which is to say - Homeland made good on its commitment to bring the story back to New York, and gave us a strong, unsettling episode tonight - or, just what you want in Homeland.
And see also Homeland on Showtime ... Homeland 1.8: Surprises ... Homeland Concludes First Season: Exceptional
more espionage in New York City