The episode begins with a perfect storm raging over Seattle. Derek and Cristina are running around with concerned looks on their faces. Five hours earlier; Hunt explains to Ethan that he and his dad are being moved to a safer hospital. They're on the rooftop helipad and Ethan and his dad are heading out to the waiting helicopter. Cristina gets a page. Meredith is in labor. Cristina finds her going through contractions. Bailey gets a chance to operate on a man who was cleaning his gutters during hurricane-force winds, but Bailey can't bring herself to start.
The hospital electricity is inconsistent and Hunt is worried. Bailey tells Hunt about her patient who is already under and she says she is not available to operate. The patient's father is standing next to Hunt and asks about his son. Webber steps in to take over. Bailey tells Hunt she wants to help in any way she can, but he says it's hard when she won't touch a patient. Callie suggests Bailey check on surplus blood supply in the ORs. Bailey leaves and Callie tells Hunt to cut Bailey some slack. Arizona gets dressed after her rendezvous with Lauren and rushes off to help with babies. She shows up to assure some parents that everything is ok. Arizona tells Alex, Jo and Stephanie to make sure the parents are all kept informed and happy. Meredith is going to need a C-section. The power goes out completely now and they all wait for it to come back.
Webber is also now operating in the dark on Bailey's patient. Hunt comes in and says he's checking on why the generators haven't kicked in. Frank, the hospital maintenance guy, is with Hunt and Webber yells at him about something he was supposed to have fixed with the electrical system. Webber asks for another surgeon to come help, but that doctor isn't available. Webber tells Shane to go get Cristina. He does. Alex tries to talk to Jo, but they're interrupted when Arizona comes up to ask Jo to check for backup batteries for the monitors in the baby unit. In surgery, Webber and Ben talk about how they both pushed Bailey too hard to come back. Cristina is refusing to operate in the dark. Webber gives her a whole speech about how this man, James, was only on that roof cleaning gutters because he was trying to help out his dad, who is old and too stubborn to move into assisted living. She relents and goes to scrub in.
Meredith and Derek talk over baby names as the doctor prepares to start the C-section. Shane and others are holding up flashlights to help provide light. The already chaotic ER gets cranked up a notch when a runaway bus flips over, crashes and catches on fire right outside the doors while everyone watches in shock. There's a gas leak somewhere but doctors and others rush to pull people from the wreckage. Meredith's pulls a baby out, but there's no crying. But soon enough there's crying and Derek holds the baby up to say he's perfect. The baby's breathing is low, though, and Derek goes with the baby to get some tests. Arizona and Alex look for batteries with no luck, and Arizona randomly confesses to having cheated on Callie with Lauren. Alex then tells her that he's in love with Jo, but he won't tell her because he's worried that he turns everyone's life to crap when he gets with them. Bailey and Leah look for meds, but the electronic locks can't be opened without power. Meredith's doctor has to go take care of another patient and one of the interns is going to have to close Meredith up. Shane goes to scrub up.
Cristina is worried she could kill the patient because the shadows keep getting in the way. Webber tells her to listen for it and orders everyone to turn their lights off and be quiet. Cristina gets her finger on the leak in the patient's heart. Arizona tells the interns to switch one baby's ventilation to manual when the battery goes out. Jo does this with ease. Two more monitors are now showing low batteries. Lauren assures Arizona that the interns and surgeons can ventilate the patients manually all night, if they have to. A moment later, an alarmed parent calls out to Arizona, asking if the flashing red light means the monitor has a low battery. Bailey comes back to the ER and sees the messy scene. Instead of jumping in, she goes back to figure out the meds. Jackson is trying to get a woman out of the bus and she's asking about her 3-year-old daughter.
Hunt says everyone is inside. Jackson and Hunt try to get the woman out of the bus. Shane is trying to close Meredith up and Heather notices a lot of blood. Meredith sees blood coming through her IV and realizes that she could have been bleeding internally after her fall on the stairs. She tells Shane to open her up again and find the source of the bleeding. She's going to have to walk him through it. She orders him not to let her bleed out on the table. Hunt and Jackson pry the woman from where she was pinned in the bus, but she can't walk out on her own because her leg hurts too much. Jackson breaks the roof's escape window. Arizona is managing the chaos in the baby unit. Shane finds the spleen is the source of Meredith's bleeding. She talks him through mobilizing it, assessing the bleeding, and stopping the hemorrhage.
After surgery, Cristina tells Webber he made her a better doctor. She thanks him. She goes to check on Meredith. Bailey is still struggling to get the meds cabinet open. Heather comes in and asks Bailey to come with Meredith. Bailey freezes for a moment, then grabs an IV stand and flails at the med cabinet until it opens. Heather and Leah are stunned. Bailey orders them to grab whatever meds they require. Hunt wheels the woman from the bus into the hospital, but Jackson sees a tiny shoe and decides to look for the little girl. He looks in another part of the bus and sees the girl sitting there, frozen. She looks at him, but won't come to him. Bailey is scrubbing in while Shane tells her he can't control the bleeding. She asks for a second set of latex gloves before stepping in.
Jackson keeps trying to coax the little girl out of the bus, but she won't come. Hunt, Callie and April look on as the bus explodes. Derek is with the baby when Cristina comes to get him. The look on her face says it all. Back in the present, Cristina and Derek are running down the dark hallway. April screams for Jackson and, finally, he emerges from the rain and smoke with the little girl in his arms. He walks by April to hand the girl to her mother. Webber looks around in the basement for Frank, the hospital maintenance man who went to check on the electrical system. He finds Frank slumped on the ground next to the circuit box and starts trying to revive him. Callie checks Jackson out for any injuries when April comes in and hits him, shouting at him, saying he could have died.
Derek and Cristina stand and talk sullenly about the baby, but Derek is worried about Meredith. Bailey comes out and tells Derek and Cristina that Meredith had a massive bleed in her spleen, but she (Bailey) removed it. She then breaks down crying. Inside the OR, Shane tells Derek and Cristina that Meredith is fine. Bailey fixed her and Heather notes that Shane assisted. Bailey thought it'd be better for Meredith to recover in the OR. Bailey comes back in and apologizes for crying and Derek gives her a big hug. Webber gets Frank sent up for treatment. Frank tells Webber he was right about what had gone wrong. Webber apologizes for having yelled at him and sends him on his way. Frank tells Webber he fixed the problem, he just has to flip the transfer switch. Webber goes looking for it.
Alex is still looking at Jo from afar and Arizona tells him that Jo did great and must have a great teacher. Lauren comes over to Arizona and asks if they're going to talk. Arizona says she made a mistake but doesn't want to talk about it right now. Lauren says she's not going to leave things like this. They aren’t able to finish their conversation because Callie walks up and interrupts them. The lights come back on and everyone breathes a sigh of relief. Then, Callie notices Arizona's ring is pinned to Lauren's scrub top. Lauren stammers through an explanation of how a baby vomited on her and Arizona was nice enough to her borrow some scrubs.
Callie is stone faced, not buying it, and glares at Arizona when she looks over her shoulder at Callie. Alex finds Jo staring out the window. He tells her he has to tell her something, but she stops him, saying they work as friends so well, she doesn't want to mess it up. He tells her he's going to say the words, right now. He then tells her that he loves her. She smiles and they kiss. April finds Jackson in his ER bed. She steps inside and closes the curtains behind her. She tells him she wants him. She starts to cry, saying she hasn't been fair to him and she's hurt him, but when the bus exploded and she thought he was gone. He reminds her that she is getting married.
She hints that she doesn’t want to get married. Callie is yelling at Arizona, saying she thought they were passed the hard stuff and were finally good. She cries while asking Arizona how she could do this. They have a massive shouting match that goes back to the plane crash. Meredith asks Derek what he thinks about Bailey, as a name for the baby. He loves it. Cristina sees them through the window, smiles, and then walks away. Ben finds Bailey and tells her he couldn't be more impressed. She's in a hurry, though. She says she needs to talk to Webber because he tried to help her and she called him a drunk. She says she owes him everything. She goes looking for him. Next to a sparking circuit box, Webber is shown lying motionless, with his jacket burned and smoldering. The episode ends at this point.