At the hospital, Meredith goes to find Mark, who is in surgery. He says he is almost done and brags about how successful he has been as Meredith waits for him to finish. When Mark discovers that Callie has been seriously injured, he rushes outside, where the doctors are waiting for the ambulance. Owen admits that they don't know how the baby is. Mark asks for a trauma gown, but Webber tells him that he has to sit this one out because Callie is his family. However, he agrees to let Mark into the room. The ambulance arrives and the doctors rush to help Callie.
Later, Alex and Lucy go to meet a helicopter. Lucy is annoyed that Webber has benched her but Alex tells her to "suck it up" as everyone just wants the best for Callie. The helicopter arrives and Addison appears. She goes to see Callie and Lucy suggests that the baby could survive if they do a C-section. However, Addison snaps that Lucy failed to stop the contractions and didn't give the baby steroids. She tells her to leave and promises Callie that she will be alright as the attendings will figure out what to do. However, when she meets the other doctors they all argue about the best way to proceed. Owen sings 'How We Operate' in an attempt to stop them arguing. In the corridor, Meredith tells Cristina that she doesn't mind if she is the godmother of Callie's baby now. Alex points out that the only way to save Callie might end up killing the baby. However, Callie and Meredith note that he has a hickey and tease him about Lucy. Alex reminds them that she works at the hospital and something is bound to happen to her because it has to everyone else.
Meanwhile, Bailey asks Arizona and Mark whether they want to take the baby out electively. Mark says that they should do whatever they have to to save Callie, but Arizona argues that it is not that simple, as Callie wants this baby. Mark reminds her that Callie could die. Soon, they are having a big argument about it. Bailey starts singing 'Wait' and Lexie joins in. Mark and Arizona continue to argue and Arizona eventually shouts that Mark is basically just a sperm donor. However, Mark yells back that he is the father and Arizona is "nothing". Elsewhere, Jackson finds Lexie and asks if she wants to go home tonight or sleep at the hospital. Lexie tearfully suggests that she might need to stay and Jackson claims that he understands because it is Mark's kid. Meanwhile, in an on call room, Derek is devastated that Callie has suffered massive head trauma and her brain may not come back. Meredith tells him to get some sleep.
In her unconscious state, Callie has a fantasy that she has returned to before the accident and is driving along with Arizona. She realises that Arizona will ask her to marry her but she doesn't answer because she doesn't know what love is supposed to feel like. She says other people manage to do it and says she wants them to be like that because she loves Arizona. She starts singing 'Running On Sunshine' and the show's other couples - Eli and Bailey, Owen and Cristina, Teddy and Henry, Alex and Lucy and Meredith and Derek - also join in as they flirt or have sex. Even Lexie sings as she sits with Mark asleep on her lap. The fantasy sequence comes to an end when Callie imagines being hit by a truck again. Back in reality, Derek lowers her sedatives to check her neurological function. However, Callie fails to respond to the tests. They go to see Arizona and Mark and admit that all Callie did was open her eyes.
Cristina has an epiphany and proposes a type of surgery to Teddy and Owen. She explains that Dr Burke taught her how to do it, explains the benefits, and reveals how they can avoid the complications. However, Teddy refuses to agree to the plan because it is too risky. Cristina turns to Owen and Teddy tells her not to ask her husband. However, Cristina says she is asking Owen as Dr Hunt, because he is in charge of Callie's case. She is annoyed when Owen sides with Teddy. Meanwhile, Arizona sits with Callie and admits that Mark is right - she's nothing legally. She adds that she feels like Callie's wife and the baby's mother and begs her to live. Callie's out-of-body self begins singing 'Universe & U'. In the corridor, Addison tells Mark to go in and make peace with Arizona as they both love Callie, but Mark says he has nothing left to say. Suddenly, Callie's monitors start beeping and they both rush in.
Later, Mark and Arizona ask Derek about Callie's prognosis. He says that when she didn't respond she might just not have been ready to wake up, but admits that it could mean her brain has been badly damaged. He leaves, and Mark apologises to Callie. He says they have a kid together and Arizona is a mother. Derek finds Meredith, who is crying in the lift. She admits that she was jealous of Callie for getting pregnant without even trying when she has struggled so much, and then the universe put Callie through a windshield. She sobs that she needs some answers. Derek hugs her and promises that they will be parents one way or another.
Arizona goes to see Callie to tell her about their daughter and says that, although she can't open her eyes yet, she knows she is looking for Callie. Callie's out-of-body self starts singing 'The Story'. As she does, Mark looks at his tiny baby. Elsewhere, Jackson finds Lexie and says he's not the sort of person to wait around for a girl who is in love with someone else. However, Lexie takes his hand and says they should go home. Meanwhile, Cristina asks Teddy if she needs her to do anything but Teddy announces that she can't teach her anymore. She says that if she refuses to learn and won't listen she can't teach and tells her to find someone else to be her mentor.
With the climax of the song, Callie's out-of-body self starts shaking Callie's bed and grabbing her legs before disappearing. Callie opens her eyes and makes a noise, making Arizona wake up suddenly. Callie says: "Yes" and Arizona asks what she's talking about. Callie tells her: "I'll marry you, yes." Arizona starts laughing as the episode ends.
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