Harrenhal. A head gets pounded onto a spike. I believe it's the guy who got the rat-bucket strapped to him earlier. But things move on and it's time for a new contestant. A soldier pulls out Gendry, because it's about time this happened to someone we care about. Once he's strapped into the chair, he says he's not from the village and doesn't know what the Brotherhood is. That doesn't stop the interrogator's assistant from loading rats into a bucket.
Just then! Horses ride into Harrenhal, led by Tywin Lannister! He's in charge here, because he's in charge everywhere he goes. But clearly no one was expecting him quite so soon. In fact, someone says pretty much that exact thing. He thinks the prisoners should be cells, rather than just penned up in the middle of the courtyard like that. The explanation is that the cells are full and also the way they're going through prisoners, they don't actually last long enough to require cells. This is not acceptable to Tywin, who asks, "Are we so well-manned that we can afford to discard able bodies and skilled laborers?" There's no answer.
Tywin asks Gendry (still in the torture chair) if he has a trade. As we know, he's a trained smith. Tywin gives the interrogator a sideways glare. This whole time, Arya is eyeing Polliver, who's wearing Needle in his belt and is surprisingly close to the prisoner pen. But then she gets noticed and is shoved away. Tywin's attention is attracted to the situation and he immediately recognizes that Arya is a girl and not a boy. He asks her why she's dressed like that and she instantly answers that it makes it safer to travel. That's a great answer. It's quick and plausible. I feel like it would be fun to see how Hot Pie reacted to this news, though. Tywin thinks it makes sense. He tells everyone to get the prisoners to work. And to "bring the girl" because he needs a new cupbearer.
Back to King's Landing! Tyrion opens the door of his chambers to discover Lancel Lannister. Lancel has a very important message from Cersei and he delivers it with all the pomp a weedy kid with great hair can muster: "Her grace the queen regent commands you to release Grand Maester Pycelle." He gives Tyrion a piece of paper with that written on it. He'd like to leave, but Tyrion wants to have some mulled wine with the kid. Tyrion muses on why Cersei didn't come herself. What should he make of that? Tyrion doesn't care what Tyrion makes of it. He doesn't want to get involved in any of that. He wants Tyrion to just release the prisoner. Tyrion wants to dig deeper: "And you've received these instructions directly from Cersei?" Yes, and he brought them straight here. He swears he doesn't delay when given an order from the queen. Tyrion continues to connect the dots: "Cersei must have great trust in you, allowing you into her chamber. During the hour of the wolf." Oop! I don't know what the hour of the wolf is (except in the context of a relatively obscure Firesign Theatre reference), but the implication is clear. The implication is that Lancel has been sleeping with Cersei. That totally happened. Now that Tyrion's got his hooks into Lancel, he twists the knife. That metaphor is not entirely right. Anyway, he notes that Lancel smells like lavender oil, which is what Cersei likes. Lancel gets flustered and protests that he's a knight. Like that's going to stop Tyrion, who was last seen talking smack to the actual king. Speaking of Joffrey, Tyrion asks if Lancel has considered what will happen with the crazy sadistic king discovers someone sexing up his mother. Oop! Now Lancel is in a panic. His only excuse is that Tywin told him to obey Cersei. Tyrion asks if the instructions explicitly included fucking. Lancel offers to leave the city at once, but that's too easy. He works for Tyrion now. Tyrion tells him, "Pleasure her whenever she requires. No one ever need know, as long as you keep faith with me." He wants to know everything. Where she goes, etc. Lancel can't object, so he's sent back with Tyrion's lavish apologies. Pycelle will be freed in the morning, but he can't be on the council.