It is pouring while Maggie is at chemo. Maggie doesn't want to be late for work.The nurse tells her to go home. Maggie won't because it's Nat's first day back. The nurse asks why she came here instead of getting the chemo at Med.

Choi is talking to some interns. Meanwhile, Noah goes into a room and finds Marcel there with an IV in his arm. Marcel takes the IV out. He doesn't know how Noah gets on his feet so soon after last call.

Charles is complaining about dealing with interns when the power goes out.

An ambulance has been in an accident. Choi goes out to help. They lift a guy, Darren, out who is screaming with pain. He says he smashed his hip. His pulse is thready.  There is also an old man with pain in his chest. They are taken to Med.

Darren is taken to Baghdad. Choi thinks they're in good shape and won't let April get something.

Natalie gets out of a taxi in the rain and rus into Med. She is glad to beback. Maggie asks how Philip is. Natalie says Philip has b een great. Maggie says but? Natalie says her memory loss may include loss of feelings. She asks how Maggie is. Maggie says her vacation was fine. 

Lanik thinks it's too soon for Natalie to be back and wants her to only do a half shift.

Marcel wants to give Mr. Lance a bypass. Lance doesn't want it. Marcel thinks it's necessary.

In private, Noah doesn't like what Marcel did. Marcel says the other option is the guy diying.

Will sees a patient who had a seizure. She says there was a gas leak at her school. She is a soccer player. She is having arm twitches. The other women with her have no symptoms. The patient says she needs to get better. Will orders tests. Then he sees Natalie standing at a computer. 

Natalie laments that everything is different. She's sorry he had to find out this way about her and Philip getting engaged. She doesn't remember it but it makes sense.

Kid with a gunshot wound is brought in. The kid is saying "they shot me." He says he was waiting for the bus. Kid needs surgery. Lanik wants Natalie to transfer him up and write the note. Maggie sees and Natalie says Lanik is stopping her from doing medicine.

Choi tells his intern about how he didn't realize his first patient was in labor. Then the lights go out... 

Emergency lights go out and Natalie is stuck in the elevator with the gunshot patient, while the surgeons working on Mr. Lance have limited time before the batteries go out on the bypass generator.

Backup generator is flooded. Chicago Fire comes to see if they can find people trapped in elevators etc.

Choi's patient may be losing blood They need to use analog tools to check for bleeds. Choi sends April to help elsewhere. Steve (Choi's intern) says  he's got it.

The backup generator is underneath a storm drain. It will take hours to get another generator. Goodwin warns Maggie today will be a marathon.

Noah is observing as Marcel works on Mr. Lance. They can't do a bypass without electricity. Noah says they are risking killing the patient. Marcel tells him to scrub in.

The GSW victim is freezing. Natalie realizes he is bleeding out. Chicago Fire finds them. But sitting the guy up to pull him out causes his vitals to go crazy. Natalie starts asking for blood and seems to forget what she is saying. Chicago Fire will get her blood ASAP and closes the top of the shaft.

Lacey is still having seizures. Her mom yells what kind of hospital is this? They can't do much because of the power failure. Lacey says the finals are tomorrow, she has to go home. Will says she can't play. Lacey cries she can't let her team down. Will says they will do their best. He goes. Dr Charles is standing there.

Maggie says they are low on fluids. New generator is taking its time getting here. Choi is called in to look at Darren. They think the hematoma has ruptured. They will have to poerate right here. Blood spurts out of his abdomen when they make an incision. Steve looks pretty sick. Choi says Steve saved his life, now come on.

Charles asks about Lacey. Will says the school says there is no gas leak. Charles wants to talk to Lacey. Lacey has another seizure just then.

Charles talks to Lacey. He sees she is doing calculus. She says the test is in a week so she doesn't have a choice. She then gets sick.

Goodiwn thinks it may be an infection. She thinks Maggie needs to get off this case given she is on chemo. Maggie refuses.

Marcel goes ahead with the surgery. Noah is nervous as he squeezes the heart. They turn on the pump and heart rate drops. Noah doesn't know how high the pump is. Noah doesn't know. Marcel says he needs to know. 5 cm. They try again.

Maggie yells at someone to try harder. April asks her for snacks for Steve. April tells Steve the patient is stable and tries to get him to eat. He says he's fine, this is just life in the ED, right? April says it's not always like this. Choi tells April to be in 3. He refuses to eat and doesn't like it that April tells Steve to eat.

Lacey pukes again. Will wants to evacuate the ED in case this is a superbug. Charles says these girls are under a lot of stress. Halstead says this is seizures. Maggie gets sick. Will says evacuate Charles wants 30 minutes. Goodwin agrees.

Chicago Fire guy says there's no blood left in the hospital. Taylor's stats drop. Nat has to intubate. Fire guy offers to do it. Natalie is having trouble. Fire guy insists on doing it. Natalie tells him after it's in to get Lanik.

Dr. Charles comes in. He says he thinks he knows what's happening and he has medicine for them. One of the girls says it's an infection. Charles is evasive about what the medicine is, saying only that it may make them groggy.

The generator arrives! Power should be back soon. Choi calls April to help him with Darren. They have to operate here Steve asks Choi if he really thinks this will work. Choi ignores him.  April charges the paddles. Choi orders Steve to use them.

Natalie and the Fire guy have to operate in the elevator. Natalie has never done this before but feels she has no choice.

Marcel gets excited that his surgery is working. The lights come on just then. Natalie can't feel the aorta. Almost got it...

Darren needs another jolt. Sinus rhythm. They need a chest x-ray. Still bleeding but vitals are holding. Bleeding has stopped.

Goodwin gets things organized now that the power is back on. Maggie is in a room by herself.

Trauma is here. Choi says to Steve we did it.

Lanik sort of gives Natalie a compliment.

Wills ays everything ame back normal on the girls. They go to the room and the girls are not twitching. Charles says he gave them Tic Tacs. The girls need therapy. Mass psychogenic illness. It was stress and anxiety.

Will sees Philip giving Natalie flowers. He finds out Maggie is okay and goes up to Natalie. He says that night it didn't feel like she was coming to say she was engaged. Natalie says she had a long day and can't talk about this. She goes. Will says wait. Does she love him? Natalie is annoyed. She says her relationship with Philip is the only thing that's working. She goes and Will watches her kiss Philip.

Noah watches arcel talk to the patient. He tells Marcel he's sorry about screwing up the pump. Marcel says are you kidding? You have a great sense of hands Noah asks if surgeons can make good money. Marcel says yeah.

Choi and April are going home. Choi says goodnight to Steve but Steve says he's not coming back. He can't do this. Choi wonders if he was too hard on Steve. April says no. She thinks they get so caught up in taking care of everyone else they forget to take care of each other. Choi says she doesn't forget. He thinks she'd make the best mom ever. They kiss.