21. 3x21 "Desire" (OAD 4/26/07)
Addison sleeps with Alex, and Mark finds out. He tells Addison that it's over because he slept with someone. Addison wants to hang out with Alex, but he tells her that she's not his girlfriend and he's busy.
George and Izzie keep running into cases of infidelity, and Callie talks to Izzie, saying that she can't compete with Izzie's friendship and to please stay away from him. George decides to transfer to Mercy West.
Derek tells Meredith that he doesn't know if he can continue breathing for her. She gets upset and leaves his trailer.
Burke tries to get Cristina to pick a wedding cake flavor, but she's just not into it.
The interns are studying for a big test.
22. 3x22 "The Other Side of This Life: Part 1" (OAD 5/3/07)
Addison takes a leave of absence and goes to visit her friend Naomi at Oceanside Medical Center in L.A. While there, she helps out with a patient. She also asks Naomi, a fertility specialist, to help her get pregnant, but the tests show that she can't have children.
Mark is mad at Alex for driving Addison away.
Meredith's step mom has surgery for acid reflux and hiccups.
Callie, Meredith, and Izzie agree to be Cristina's bridemaids. Her mother and Burke's mother show up to plan the wedding, and Burke tells his mother that Cristina is not cold.
23. 3x23 "The Other Side of This Life: Part 2" (OAD 5/3/07)
Susan is rushed into surgery for sepsis. Meredith tells her that she's going to be fine. Meredith comes out crying and tells her father they did everything they could. He shakes his head and then he slaps her.
Burke tries to convince his mother that Cristina is right for him and she says that if Cristina is so right, then why is he yelling at his mother?
Izzie tells George that she doesn't want him to leave. It's not fair that she has to lose her best friend. They kiss until George pulls away.
George continues to wonder if he's made a mistake marrying Callie. He asks Burke if it's possible to be in love with two women at the same time.
At Oceanside Wellness, they invite Addison to stay and be part of the practice, but she declines.
24. 3x24 "Testing 1-2-3" (OAD 5/10/07)
Meredith's father comes into the hospital and tells her not to come to Susan's funeral. He and Susan trusted her and she killed Susan.
The interns take their first year medical exams.
Burke's best man is not able to make the wedding so Burke asks Derek to be his best man. Derek throws an informal bachelor party at Joe's.
Adele comes to the hospital and talks to Addison because she is pregnant. Richard sees her and she goes into the bathroom. He says things through the door, but when she doesn't answer, he goes in and finds her on the ground, bleeding.
George gets a position at Mercy West, and Izzie tells him not to go. Bailey is hurt that he would leave after they've put so much time into him.
25. 3x25 "Didn't We Almost Have It All?" (OAD 5/17/07)
When Adele wakes up, Addison looks for a heartbeat, and finds it, but then has to do a D&C. Richard stays with her. Adele tells him that he is the father.
Cristina freaks out when it's time to go down the aisle for her wedding, but Meredith talks her down. Burke goes to Cristina and she says she is ready. He says that he is trying to change her and then he leaves. Meredith has to announce that the wedding is over, and it seems that she and Derek might be over as well.
The interns receive their exam results and George didn't pass. Callie was named chief resident and talked George into having a baby with her.
While George cleans out his locker, the new interns come in. One introduces herself as Lexie Grey.