Stannis Baratheon attacks King’s Landing! That’s the entire storyline this episode. We don’t go to the Wall, we don’t go to Qarth, we don’t check in on Arya or Theon or anyone. If you’re not in King’s Landing or attacking it, you don’t get to be in this episode.
The overall attack is stopped, thanks to Tyrion’s boat full of wildfire and a timely speech that comes right after Joffrey abandons the defense of the city. Even so, Stannis is about to win when Tywin Lannister rides in and saves the day. Cersei was about two seconds from poisoning Tommen, so it’s a good thing she spent a long time telling a story about lion cubs.
During the battle, the Hound has a flashback to the time his face got burned and decides to give up the whole deal. He walks out on the battle, which is probably a good idea. Out in Stannis’s fleet, Davos and his son aren’t so lucky, since they’re on the boat closest to the giant explosion. I mean, they might have survived, but I wouldn’t bet on it.