Now that Teddy is starting to come to grips with her widowhood, she needs to get out of the house with the girls for a fun night, as suggested by Callie, and she wants to go to a fancy restaurant. Callie forgot to mention this to Arizona, but she agrees to go along and has Callie invite Bailey too, so Teddy doesn't feel weird just going out with a couple. Bailey grudgingly agrees until Ben points out that he has a sexy evening in store for them since it's the first evening they've had alone in weeks, and then she cancels with a very lame excuse. Callie sees right through her and just about talks Arizona into bailing for the same reason, and on top of that Mark can't babysit so they can't leave the house anyway. Just as Arizona is about to cancel, Teddy talks about how excited she is and gets worried that maybe they don't want to go, so Teddy runs over and tells the other ladies that they are being horrible friends and they have to do what they originally promised. They wind up doing an evening of wine and movies at the Torres/Robbins apartment and also restore their standing as good people and friends.

The residents are all panicking about the Boards and decide they need to study some real cases and not just hypotheticals off of flash cards. Alex tries to sneak a bunch of charts from the library but he's caught, and told that the files don't leave the room. He gets the brilliant idea to have the Lexipedia read everything and then quiz him and when the others catch wind of this, they bombard her with files too. Everyone, that is, except for Mere who is totally and awesomely prepared because Callie's method really is that good. Lexie basically turns into a pile of mush from info overload so Mere forces everyone to leave her alone, but then calls all of them over to her house to start her own tutoring method; they will all sleep and eat and spend every moment they aren't at the hospital at Mere's house studying as a group.

Cristina and Owen are both out with the "flu" (more on that later) and so Mark is Chief for the day, since Owen asked for him by name to fill in. He takes it crazy seriously and gets very annoying, very fast. Derek and Ben have a very complicated surgery to do that they both think is too dangerous, but Mark just orders Derek to come up with a solution. Derek manages at the last minute to have a genius idea involving the use of a bean bag chair, Mark beams at how he brought out the best in his friend, and the surgery is successful.

Mark also butts heads with Richard but this time it's because Richard wants to proceed with a surgery and Mark orders him not to -- the patient is a man who needs a multi-organ transplant, and isn't going to make it much longer without those new innards. They get the organs for transplant but see that there is a spot on the liver, and Mark declares that this makes the organs unsuitable and they have to reject them and put the guy back on the list. Bailey has the idea to operate on the donor, who is still on life support, and to take out the tumor and see if it's benign or not, which Richard thinks is brilliant, but Mark forbids it and as Chief, his is the final word. ...Except that, as former Chief, Richard is willing to go behind is back and make it work. Mark finds out what is going on and storms into Richard's OR, where he has just removed a completely benign tumor and so all of the organs are now good to go. He points out to Mark that as a plastic surgeon he's used to everything being perfect and pretty but as Chief, sometimes you have to be creative and just figure out what will get the job done. In this case, if the guy didn't get these organs, he would die, so this was the way to make them suitable. Mark grudgingly agrees to it, the patient gets his organs, and all is well.

Oh, and much later, when Derek finds Owen playing a little bit of rooftop golf, it comes out that Owen asked for basically anybody but Mark to fill in for him that day. But Derek admits that Mark did a good job, while swearing Owen to secrecy that he admitted that.

Back to the "flu." Cristina and Owen have both called in sick because they are in the middle of a massive fight at home. Actually, "showdown" might be a better word than fight. Whatever you call it, it's not good -- Cristina is demanding to know the details of Owen's cheating, but he thinks this will just hurt her even more and doesn't want to tell her. She gets him to eventually get out most of the story, which we get in drips and drabs over the episode. The nutshell is that he met the woman when her friend was brought in to the ER.

After saving the friend's life, the two of them were drinking at Joe's, got drunk, he walked her home, she flirted drunkenly, he tried to talk himself out of it at first, but then, obviously, he didn't. He assures Cristina that it was just sex and in fact can't even remember the girl's name, but she thinks this is worse than if he'd been in love with someone else -- she could understand if he just couldn't help himself because he loved another. After lots of sobbing, sitting, locking oneself in the bathroom, and finally some talking, Cristina realizes that Owen did it to hurt her; to pay her back for hurting him. And I don't know if that was his conscious intention when it happened, but he doesn't deny it. And this leads to Owen moving out.

Mere had called Cristina earlier in the day to make sure she was okay and calls again after work, which is after Owen has left. Cristina can barely talk; she just sits on the phone while Mere assures her she'll stay on the line as long as she needs until her. Cristina can't take it and hangs up fairly soon thereafter, but winds up showing up at Meredith's house later, admitting that she's possibly going to fail her boards (because with all of her personal drama, she hasn't been studying) and she joins the gang as another study buddy. She may be brokenhearted but in the ten seconds we see of her, she looks more like herself than we've seen in weeks.