Kingslayer

Why

Jaime was locked back in that claustrophobic, ugly room after a long and heated argument between him and his father, which the elder Lannister had ultimately won in end.
Aside from Baelish none of the other onlookers had contributed anything. Cersei was smug. Tyrion worried. Varys impassive. Jaime was still angry with his father and Tywin with his son. They were at a stalemate.
As Jaime was being escorted back, he saw both Tyrion and Cersei begging thier father to be allowed to see him, for completely different reasons. Tywin had refused. He knew his children too well. He knew they would try to help their brother escape or would bribe the guards with money. Everybody wanted a slice of the Lannisters' fortune.
Kyra's fate was also undecided. Tywin had given her for the moment the same treatment as Jaime. Maybe not quite as harsh. She had her own chambers and guards but her door was unlocked and she was free to roam the Red Keep if she was escorted. Her father was one of his bannermen. If he treated her badly, he would use a valuable ally. He could ensure the destruction of thier House, but that would have disastrous consequences in the long run.
It was more than she could have asked for. Tywin had also made sure she, at certain hours of the day, lent her services to Pycelle. He wouldn't waste a good medic. Tywin couldn't touch her.

Jaime on the other hand was his son. Jaime was completely under Tywin's control. And Tywin ensured his son knew as much. Jaime was incredibly frustrated. Hours on end staring at the same four walls. He'd had enough of that already. Soon, there was a knock on his door.
"What?" Jaime snapped without turning round to see who was coming in, knowing it would be a guard, presumably with the message that his father wanted to see him. Couldn't Tywin leave him alone? Just for a bit?
"Nice to see you too." That wasn't a guard. It was Tyrion. He shut the door.
"Sorry. How did you get past them?"
"Gave them a large bag of gold each. More than they get paid in a year."
"And father?"
"He's away for two days. Some issue in the Westerlands. He's decided to deal with it himself. But don't think that means you're getting a free pass. Joffrey's here and he has Ilyn Payne taking command of your guard. It just means, that because father's away, the guards are more susceptible to being bribed." Jaime took a seat, Tyrion the other.
"Why is it every time we talk, I'm locked up as a prisoner?"
"I must be cursing things for you. What did you say to father that got him so angry he felt the need to keep you in here guarded anyway? He refused to say."
"When I was still recovering I asked his permission to do something. He never gave me it. But I went anyway. When I returned he put me in here and that was it."
"What were you doing?"
"I rode to the Stark camp and spoke to Kyra."
"Are you insane? You almost died in that place! You were chained and beaten up and you wanted to go back there? No wonder father refused you. I mean, I don't particularly like him but t have to agree with him on this one unfortunately."
"He didn't know I was going there though."
"Doesn't matter."
"How is she anyway? Have you seen her?"
"I spoke to her in passing on my way here. She was asking for you. As far as I know she enjoys working for Pycelle."
"She's the only one who likes his company," Jaime muttered. "It can't be that long he keeps me in for, can it?"
"You know father. No one has any clue what's going on in his mind. Who knows what he's thinking?"
"Because that's so helpful," Jaime retorted. Tyrion saw that his brother was very angry. "I would ask you to get me out but father would come after me with everything he had and my situation would just be made a hundred times worse."
"I'm afraid you're probably right. It's better to wait this one out." Jaime sighed.
"This is driving me crazy. I've not properly wielded a sword in over a year. I'll lose the practice of I don't."
"Jaime, one thing you're never going to forget how to do is fight. It's in your blood. If you keep on the right line with father you'll be let out quicker."
"I don't know."
"You're his favourite. Trust me."
"I don't know. I've messed everything up this time."
"You haven't. You saved Kyra. She's happy."
"At least someone is."