Lancel (favoring his shoulder) runs up to Joffrey and says that the queen has sent him to bring Joffrey back to the Red Keep. Man, lay off Joffrey. He's having a hard enough time without this going on. Tyrion asks Joffrey, "If you won't defend your own city, why should they?" Joffrey is torn and actually asks Tyrion for advice. Tyrion tells him to lead. He should get down there and lead his people in their defense against the invaders. Joffrey asks if his mother had urgent business. This is obviously where Lancel is supposed to make something up to give Joffrey a good excuse for leaving, but Lancel is a literal-minded simpleton so he says no. Joffrey leaves anyway and a lot of people watch him do it. Tyrion is not impressed, even though Joffrey does leave a couple knights with him. I think Joffrey probably would have stayed if Lancel hadn't showed up to tell him to retreat.
Some of Stannis's men (and Stannis) are on top of the wall, which results in some rocks falling inside the city. We see the people of King's Landing asking where the king is and who leads them. Podrick runs up to Tyrion.
Tyrion announces, "I'll lead the attack!" The people are unimpressed. He takes his helmet from Podrick and has one of Joffrey's knights unfurl the King's banner. He shouts "Men!" a few times, but the crowd is dispersing and giving up. "They say I'm half a man. But what does that make the lot of you?" A voice from the crowd says that the only way out is the gate, which is where the enemy is. Well, that can't be true, can it? Surely there are other gates. There's the King's Gate, for one. Podrick just removed all the guards from it, so you guys could probably escape if you really wanted to. Tyrion says there's another way out that he can show them. And then? "Come out behind them and fuck them in their asses!" The noise of the battering ram gets louder. "Don't fight for your king. And don't fight for his kingdoms. Don't fight for honor. Don't fight for glory. Don't fight for riches because you won't get any. This is your city Stannis means to sack. This is your gate he's ramming. If he gets in, it will be your houses he burns. Your gold he steals. Your women he will rape." The battering ram continues. The gate cracks. "Those are brave men knocking at our door. Let's go kill them!" Wild cheering. Everyone's in. Tyrion walks down among them and they all follow. It was a good speech and very in the tone of this show.