"Now or Never" is the twenty-fourth episode and the season finale of the fifth season of the American television medical drama, Grey's Anatomy and the show's 102nd episode overall. Written by Debora Cahn and directed by Rob Corn, the episode was originally broadcast on the American Broadcasting Company (ABC) in the United States on May 14, 2009. The initial airing was viewed by 17.12 million viewers and garnered a 6.2/17 Nielsen rating/share in the 18–49 demographic. The episode received widespread critical acclaim, with particular praise directed towards Katherine Heigl's performance. It marked the last regular appearance of original cast member T. R. Knight, who played Dr. George O'Malley who got into an accident during the episode and dies in the season 6 premiere. He later returns in season 17 as part of a dream of Meredith Grey.
In the episode Cristina Yang (Sandra Oh), Alex Karev (Justin Chambers), George O'Malley (T. R. Knight), and Meredith Grey (Ellen Pompeo) are all sleeping and waiting for Izzie Stevens (Katherine Heigl) to wake up after a surgery to treat her cancer. Derek Shepherd (Patrick Dempsey) comes up with an alternative treatment plan for Izzie, Miranda Bailey (Chandra Wilson) confronts the Chief, Richard Webber (James Pickens Jr.), and Arizona Robbins (Jessica Capshaw) about the paediatric fellowship program. Yang deals with her relationship with Owen Hunt (Kevin McKidd), who helps George with career advice and influences his choice to enter the US Army. This episode also focuses on Meredith and Derek's post-it wedding.
Plot
Cristina is still deliberating reconciling her relationship with Owen, however she has not completely forgiven him. Owen stops to tell her how well his therapy is going and how much progress is being made, but Cristina cuts him off by asking if he's told her about not visiting his mother even though she lives only a few miles away.
Derek has formed a plan to remove Izzie's brain tumor, but it will require removing a part of her brain, which could leave her without any memory. Izzie tries to get the others to decide, but they only offer to support her unconditionally with her own decision. However, they later decide to find out more information in order to make an informed decision. To see the worst possible outcome of the surgery, the doctors agree to run a neurological test. During the test, Izzie cannot remember the pictures on the flashcards or other people and she can’t even speak. This unsettles Meredith, who tells Izzie that she cannot possibly have the surgery. Izzie eventually decides to have the surgery, but signs a Do Not Resuscitate order to avoid the possibility of being in a vegetative state. Alex, who had spontaneously married Izzie earlier in the season, panics about the idea of living without her.
Later on, Cristina sees Owen hug George and asks what's wrong. Owen tells her that George has some news but he wants everyone to hear it from George himself, then changes the subject, saying he’s happy that he finally slept through the night with no nightmares.
Chief Webber calls Bailey into his office with Robbins to tell her that she's received the pediatric fellowship. Rather than being excited, Bailey simply walks away. She later tells Robbins and Webber that her husband, Tucker Jones (Cress Williams), gave her an ultimatum the night before - if she takes the fellowship, he will divorce her. She plans on leaving him, stating her belief that there is no place for ultimatums in a marriage, but doesn't think she can do the fellowship as a single mother. Instead, she decides to stay in general surgery with hopes to become an attending.
Meredith and Derek have decided not to wait any longer to get married and go to City Hall that evening, but later realize that they won’t make it in time. Instead, Derek writes their vows down on a post-it note that they both sign and then stick in Meredith’s locker.
Meanwhile, a John Doe is brought into the ER who was hit by a bus in order to save a stranger, injuring his face beyond recognition. The woman he saved is called Amanda (Shannon Lucio), and she keeps checking on him and calling him "her hero", "Prince Charming" and similar names. When Meredith checks on John Doe, he attempts to trace something on her hand that she doesn’t understand, so she tries to get him to hold a pen; however, he is too weak and Meredith says that he can try again later. Eventually, John Doe successfully traces the numbers “007” on Meredith’s hand, referring to George O’Malley’s nickname that he earned in the show’s first season after freezing up in his first surgery. Meredith realises that John Doe is George, and runs to tell the other doctors; they rush him into the operating room.