Derek figures out a way to get to Izzie's tumor. He wants to remove part of her hippocampus, a common surgery for seizure patients, but one that could affect her memory and her speech. Given the severe possible side effects, Izzie is reluctant to go that route. Dr. Swender wants to try her on IL2 medicine, which has kept her "miracle" patient alive and tumor-free for two years.
To see how Izzie's memory might be affected by the surgery, they do a test where they show her flashcards and then ask her to say what was on them, repeating it with the right half of her brain has been put to sleep. She's unable to speak or even nod when Meredith asks her to tell her who Alex is. Dr. Swender and Meredith are adamantly opposed to the surgery and after talking to the IL2 patient, Izzie decides to try the less radical approach.
Alex wants to know what Derek would do: "What if it was Meredith?" he asks. Derek tells him, "I would ask her to have the surgery."
Owen tells Cristina he's had a good session with his shrink, but she wants to know when he's going to tell his mother he's back from Iraq. George works with Owen on a patient, an ex-soldier with constant, excruciating pain in his leg. The doctors can't find anything wrong, but the soldier wants them to cut if off so he can get back to Iraq. George asks the soldier why he wants to go back so badly and he explains that he has nothing in common with his relatives and that the guys in Iraq are his "real family."
Arizona wants Miranda to scrub in with her on a pediatric case, but Richard lures her back to general surgery with his newest acquisition: A high-tech robotic operating system. She absolutely loves it and eagerly jumps at the chance to do a second surgery with the hospital's new toy. Arizona vows to fight the Chief for Miranda's time.
Alex can't believe Izzie has decided against the surgery. "It's not just your life at stake anymore," he shouts at her. "You're having the surgery!" Derek is furious with Cristina for talking Izzie out of the surgery, until Meredith tells him she's the one who talked to Izzie. Meredith tells Derek how her mother wasn't her mother anymore once she got Alzheimer's, how she lost her dignity, her memory. Derek insists it's not the same thing, and that Izzie's condition is treatable. He orders Meredith, as his resident, to go back and talk Izzie into the surgery.
Izzie is talking over her decision with the IL2 patient when the woman collapses. Surgery doesn't go well and Izzie looks on as Swender tells the woman's family that there is no hope she'll ever be off a ventilator.
Izzie pages George to ask him what to do. "You know what to do," he says. "You've already made the decision." Izzie tells Derek he can operate, but she doesn't want to end up on a ventilator. She signs a DNR but Alex wants her to tear it up. "I can't live like this," she says. "And I can't live if something goes wrong. It's not what I want." She says she "went crazy" when Denny signed his DNR but begs Alex not to do the same thing. "If it comes down to it, just let me go," she pleads.
Owen tells Cristina he's decided to go back to Iraq, and that his nightmares are the result of "unfinished business." She tells him she doesn't want him to die. He asks her, "Come with me," and they end up on his mother's doorstep.
It's a different doctor who knocks on the army recruiter's door: George, who's inspired by the soldier's passion.
The soldier talks Callie into amputating his leg but she freezes when it comes time to cut. "We're not doing harm. We're saving him," Owen tells her.
After seeing Izzie wheeled off to surgery, Meredith says to Derek, "Let's go to City Hall tomorrow. I don't want to spend another day not being married to you."
After the surgery, Izzie wakes and is told she's fine, apart from "sluggish" kidneys. She is jubilant when Derek tells her he got the whole tumor out. But then she asks again about how the surgery went. And again. "Did you screw up her brain?" demands Alex, but Derek asks him to stay calm, that this could just be a temporary post-op condition.
Since Derek and Meredith are getting married, and won't want housemates anymore, Mark asks Lexie to move in with him. When she says she wants to wait several years, at least, he takes a patient's advice and tells her that he's "moving on" and that he's going to buy a house on his own.
After the visit to his mother, Owen tells Cristina he slept without any nightmares for the first night since he's been home. "I'm getting better," he tells her, and asks her to think about taking him back.
George stuns everyone with the news that he's joined the Army to be a trauma surgeon. Miranda and Callie plan an intervention for later that day to stop him from reporting for duty the next morning. Arizona doesn't understand why they have to stop him, saying it's "awesome," that he's joined up. Callie can't believe Arizona won't back her up and asks, "Who are you?"
Arizona demands to know why Miranda isn't jumping for joy at the news she's been awarded a prestigious pediatrics fellowship. Miranda explains it's a big decision: If she accepts the job, along with the extra hours of training, her husband will divorce her.
A severe trauma case comes in: A man who jumped in front of a bus to save a woman he didn't even know. The team works on him frantically, debating whether they can save his arm. His skull is bashed in, so he can't speak and he has no I.D., so they dub him, "John Doe." The woman whom he saved tells Meredith how she was mean to him, just before he saved her life, but now she's decided he's her Prince Charming, and refuses to leave his side.
During surgery on John Doe, Owen wonders how George will do in Iraq. "You think he can handle it?" he asks and Callie says, "No, I don't." But Derek says, "I think he's going to surprise us all," and Mark predicts, "He's coming home in a body bag." Meredith asks them all to "shut the hell up."
Alex starts writing down vital infromation on notes for Izzie, notes like, "Derek got the whole tumor out." And "Your memory sucks." He repeatedly quizzes her on details like what time she got up, but she can't remember any of it. Cristina tells him that Izzie needs to rest, but Alex believes she needs to exercise her memory, "before it all turns to mush." Cristina threatens to ban Alex from her bedside if he keeps badgering her and he insists that Izzie's future depends on him.
Cristina wants to know if Meredith is happy, if the therapy worked. "Are you better now?" she asks. Meredith confesses she's getting married today and Cristina hands her something new (a pack of Post-its), something borrowed (a pen), both blue. After lamenting about Izzie's condition, Meredith says, "It's important to tell the people you love how much you love them while they can hear you." She smiles and says, "I love you Cristina Yang." "You have changed," says Cristina, who goes to tell Owen that she loves him and that she "can't breathe without you." Owen tells her, "We can do this. Just meet me halfway. All you have to do is say yes."
Arizona tells Callie why she thinks George enlisting is a good thing: "My brother died because there weren't enough doctors over there. So for my money, George O'Malley is a patriot. So yeah, the word I use is awesome. That's who I am." Callie stops her from leaving the room and apologizes.
Alex keeps drilling a fatigued and confused Izzie until she tells him to back off. "You made me promise you that you wouldn't live like this," he shouts. "So now what am I supposed to do? Smother you with a pillow?"
Miranda asks Richard if there's still a spot available in general surgery. He can't believe she's asking to come back when he's finally given her his approval to join pediatrics. "Tucker gave me an ultimatum: My fellowship or our marriage," she explains, saying she's going to leave him. But she has to turn down the fellowship because now she's going to be a single mom.
Meredith panics because there isn't time to get married, between watching Izzie, George's intervention, and all their surgeries. Derek tells her they can get married another day, but she replies, "There is no other day. Every day is like this. Every day is a crisis. I love you and I want to marry you today, but there is no time."
He asks her if she has a piece of paper and suggests they write their vows right then. She hands him a blue Post-it. "What do we want to promise each other?" "That you'll love me even when you hate me." "No running," Derek suggests. "We'll take care of each other even when we're old and smelly and senile. And if I get Alzheimer's and forget you," she adds and he says he'll remind her who he is every day. He writes it all on down and asks her to sign. "This is our wedding? A Post-it?" she asks, but she signs it and Derek says, "Now I kiss the bride."
Izzie unloads on Cristina about how Alex threatened to smother her with a pillow and they both realize that she's got her memory back.
Cristina finds Owen and tells him, "Yes."
Callie and Miranda are stunned to learn that George has already left the hospital: Richard told him to take the day off and spend it with his mother.
John Doe tries to communicate with Meredith. He spells out "007" in her palm. She realizes with a shock who he is: It's George!
Alex gets the news about Izzie's memory having returned and joyfully hugs her, saying, "You're back," but she collapses in his arms. Alex tries to revive her but Cristina reminds him that she'd signed a DNR. "Alex it's not what she wants," she says, but he keeps working on her. "Screw the DNR," Richard shouts and they all try to bring her back.
We see Izzie, in the prom dress she wore the day Denny died, get into the elevator. The door opens and George is waiting for her in uniform.