Tyrion and Cersei have put their differences aside long enough to commiserate about the marriages they're being forced into. They wonder if killing Sansa and Loras would solve their problems. I think it probably wouldn't, given that part of Tywin's motivation appears to be a wish to make his kids get in line. Tyrion thinks all four of them (himself, Sansa, Cersei and Loras) are getting it bad, but Sansa is probably getting it the worst. I don't know; Tyrion is still part of the royal family and there's a pretty good chance that Sansa's self-delusion field is strong enough to convince her that it's still romantic. Cersei says she did her various vicious acts to protect their family. Tyrion points out that he should count as that. Cersei is in a generous mood and is willing to admit, "If it weren't for your trick with the wildfire, Stannis would have sacked the city before father got here. Our heads would still be rotting o the city gates." Tyrion suggests that she tried to have him killed on the battlefield by instructing a member of the Kingsguard to kill him. The he asks her directly if she did it since there are only two people who can order the Kingsguard around. She doesn't answer. Tyrion sighs, concluding that it was Joffrey, not Cersei: "The impulse I understand. He hates me because I'm the only one who tells him what he really is. So. Fair enough. He wants me dead." Tyrion thinks poisoning him would have been smoother, rather than having a member of the Kingsguard kill the Hand of the King in front of two armies. Tyrion wants to know if his life is still in danger. Cersei thinks it probably is, but not from Joffrey. I don't know if she has anyone specific in mind. She might just figure that everyone's life is always is danger. She wouldn't be wrong.
Cersei thinks that soon, "Joffrey will belong to Margaery, the little doe-eyed whore," so all his decisions will be whatever Margaery tells him. Rather than "whatever Cersei tells him" like it's supposed to be. Her bigger concern is that Joffrey's children will belong to Margaery. Oh well. Tyrion thinks Jaime might kill Loras when he gets back, but Cersei doesn't know when that will be. Her opinion is, "Jaime or not, I'm truly fucked." Cersei asks who's going to tell Sansa about the new plan. Why tell her at all? Just throw her in a gown and surprise her at the wedding. It's not like she's being given a choice in any of this. You know, Edmure Tully needs to get over himself, since everyone else in the world is also being forced to marry against their will.