Here's what I know. There are some lines too dangerous to cross. But there are others - if you're willing to throw caution to the wind and take a chance, the view from the other side is spectacular.
Meredith doesn't want a relationship with Derek, but in a moment of weakness when it's just the two of them alone in an elevator she kisses him. Alex gets switched to Bailey's team of interns, forcing him to work closely with those who hate him most. He and Cristina get assigned the seemingly simple chore of delivering good lab results to patients and their families, but they quickly find themselves bombarded with hugs and tears of joy two things they simply can't handle. Izzie gets to practice "actual medicine" sewing up minor cuts and injuries. One patient, though, who doesn't speak any English, becomes troubling to Izzie, as the patient desperately tries to tell her something and just won't leave. Bailey assigns George to run the code team, responsible for shocking patients on the brink of death back to life when their vital signs crash. And when not fending off the advances of Derek, Meredith is put in possession of a bit of evidence retrieved from the body of a rape victim the attacker's penis.
Burke's world is turned upside down when he realizes that he isn't Richard's top surgeon anymore. Richard feels Burke's gotten too complacent, and has brought in Derek specifically to compete to be his replacement one day. This leads Burke to take Meredith's side when she wishes to interfere with a patient in another service (a big no no usually). Meredith thinks a baby might have a serious heart defect, but the pediatric intern actually caring for the baby strongly disagrees. Turns out, Meredith is right, but Burke still scolds her for using unorthodox tactics to get around the pediatric intern (i.e. going straight to the baby's parents).
When the rape victim's attacker stumbles into the hospital needing emergency care, Bailey gets to make the call without a hint of sadness that reattaching his penis isn't possible. Izzie finally finds out what the non English speaking patient needs her daughter is outside, also needing medical attention, but is afraid to come in because she doesn't have a green card. Izzie helps the both of them, stitching up their wounds outside the hospital, even though it's way against hospital policy to do so (and could Izzie in much trouble). Failing to save any lives, George learns the sad truth that being on the code team means of all patients are beyond recovering by the time you even get there. And Cristina and Alex don't really learn anything at all, except that they'd rather be doing anything else all day than delivery lab results.
Derek spends a great deal of time by the rape victim's bedside, revealing a softer side to Meredith (the victim has no friends or family in Seattle), but it's not enough to win her over. When given the option to ride in another elevator alone with Derek, she opts to take the stairs.