This week's episode is all about people from the past turning up like a bunch of bad pennies. First, we discover that Susan has gone into maternal overdrive with Meredith, constantly showing up at her house and buying her groceries. As you would expect, Meredith reacts by telling Susan to back off. But Susan is persistent, and ends up forcing Meredith to admit that she kind of likes having Susan around. And then Crush's parents show up after her new face is splashed around the news. She's pretty excited, but Alex is clearly not happy about letting her leave. Fortunately for him, her parents decide they're not really her parents after all, leaving her at the hospital. Unfortunately for him, Crush is kind of pissed off about this, and she takes it out on Alex.

Colin Marlowe also shows up, to convince Cristina that she's with the wrong man and generally lord his cardio-godhood over Burke. Cristina fights back by acting disgustingly girly in order to convince Marlowe that she's really committed to Burke. This actually works when Marlowe decides that Cristina is no longer the woman he once loved, and he departs the hospital and the show.

The last person who shows up unexpectedly is Izzie's daughter. Yeah, I know! She has leukemia, and her parents ask Izzie to consider donating bone marrow. Izzie is overcome with emotion, and ends up telling the whole story to Bailey, who is as kick-ass and supportive as you would imagine. Izzie agrees to donate the bone marrow even after her daughter refuses to meet her. George, who has still been giving Izzie the cold shoulder after the awful, awful sex, gets suspicious that something is up and ends up butting into Izzie's marrow donation. This rekindles their friendship, but throws some cold water on George's relationship with Callie, who catches him lying about where he was for the day.

And in a storyline that really doesn't fit the metaphor about people from the past turning up, Derek continues to push Weber about winning the Chief's job. Weber is not especially supportive, and it turns out that he thinks that if Derek becomes Chief of Surgery, it will ruin his relationship with Meredith. This leads Derek to think that he has to choose between Meredith and his career. So we'll all see how that turns out.