Continuing where last season's finale left off, Carter returns from Africa, going straight to Abby's bedside. Her response to seeing him is to ask for her key back. She is very chilly towards him all day until new med student Neela Rasgotra answers a phone call for Carter. The message: Luka is dead. Carter decides to go back to the Congo to bring the body back. Abby pleads with him to stay, but he leaves anyway. Neela has a tough first day in the ER, earning Chen's ire after Pratt flirts with her. Gallant, now a full-fledged doctor, helps to show her the ropes though. Romano returns from his medical leave. Susan is still seeing Chuck. Weaver screams a lot.

The episode was rated 7,57 from 84 votes.

Good samaritan Luka stops to help a woman with a flat tire, and watches her get hit by a reckless driver. Abby discovers that she passed her boards. Pratt is concerned about Chen when she comes to work with a black eye. Neela heads for the University of Michigan to begin her internship but decides not to follow through. When Steve announces his intentions to stay in Chicago, Sam decides to leave town. The custody battle for Henry Lopez goes before a judge. While Pratt drives Elgin Gibbs home en route to dinner with Chen, the three are shot at by an irritated driver.

The episode was rated 7,59 from 80 votes.

Luka's first day back in the ER is a busy one. While working out the details of his return with Weaver, he mentions that he'll be returning to the Congo in two months. Lewis treats an alcoholic mom who sets herself on fire in front of her son, and an elderly architect who tried to commit suicide because he's going blind. Abby appears as a surgical consult; she's back in med school. Sam Taggart replaces her on the nursing staff. Dorset's wife calls while he's in surgery with Corday.

The episode was rated 7,62 from 79 votes.

Morris streets a patient without getting a psych consult, and the guy steals a tank and heads for County. Gillian is visiting Luka, and Sam's not happy about it. Frank finds himself fighting for his life after suffering a heart attack with Neela and Pratt the two unlikely doctors who successfully save Frank's life. In the process, surprising facts about Frank's life are revealed, including the deep respect he has for the colleagues he puts down on a daily basis. Corday plays the dating game, going out with two men.

The episode was rated 7,64 from 78 votes.

Carter reunites in the Congo with Charles and Gillian. Through flashbacks, we see Luka after Carter left 22 days before. He has caught malaria, and is soon captured by Mai Mai, who begin to murder the people he's with. Gillian introduces Carter to Debbie, a worker for the Red Cross. They search for Luka, and when finally shown the body, it's not him. Carter learns that the rebels mistook Kovač for a priest and left him alive. Carter, Debbie and Gillian find Luka, nearly dead, and put him on a plane back to Chicago. Carter gives him a letter to give to Abby and the news that he's going to stick around in the Congo for a while.

The episode was rated 7,67 from 78 votes.

Kem accompanies Carter to work and manages to annoy about half the hospital over the course of the day. Weaver has used the money that Romano left to the hospital and unveils the Robert Romano Center for Gay, Lesbian, Bi and Transgendered Health Care. Gallant is doing a ride-along with Morales and Bardelli. Weaver offers Lewis the acting ER chief job, but Susan refuses because she's pregnant. Pratt is questioning his abilities as a doctor. Chen calls the ER to tell Pratt that her mom has died in China. Sam finds out about Luka's reputation as the ER bed hopper, but finds herself making out with him by the end of the day.

The episode was rated 7,67 from 70 votes.

New residents arrive at County, including 2nd year Nick "Coop" Cooper. Coop talks back to Romano and is nearly killed when Neela gives him too much epi during an asthma attack. Abby's frustrating day starts with an awful round of managing triage and gets worse when she gets a special "Dear John" letter from Carter in the Congo while her fellow nurses threaten a walkout and her opinions are ignored. Romano's mood gets nastier when he is fitted with an antiquated hook for his missing arm. Pratt uneasily meets Chen's old-fashioned parents for dinner in what turns into a last supper for their relationship.

The episode was rated 7,68 from 77 votes.

Since his return to County, Luka has become obsessed with treating and streeting patients as quickly as possible. He argues with Pratt over the treatment of a pregnant woman who doesn't want her premature baby, as well as with Romano, who wants more tests ordered on patients so that the hospital can make some money. Abby is still on her surgical rotation and Romano is riding her hard. Coop flirts with Chen. Susan has been reading to Ben Hollander in her spare time. Luka meets Sam's son Alex in the new JumboMart (which has replaced the fire-damaged Doc Magoo's).

The episode was rated 7,69 from 77 votes.

An entire family suffering from carbon monoxide poisoning is brought to the ER. Claustrophobic Neela must spend a couple of hours in a hyperbaric chamber with the newborn baby. Carter misses Kem, who's been gone for a month now, so Jerry arranges a webcam chat for them. Alex finds out about Luka and Sam. Sam then suggests they take their relationship slower, Luka isn't too thrilled. Dr. Lawson asks Elizabeth out. Sandy's mom brings Weaver's son Henry in. Chen returns from China: her dad needs 24 hour nursing care and she's having trouble getting adjusted to that idea. Susan and Chuck visit her dad and tell him about the pregnancy.

The episode was rated 7,71 from 72 votes.

Gallant's sister is in town and Pratt hits it off with her. Nobody attends Romano's memorial service except for Corday. Alex steals a severed finger and later goes missing, turning up at County to see Luka. Neela treats two Amish kids who were injured on a sojourn into the city.

The episode was rated 7,75 from 81 votes.

Neela and Abby face their toughest rotation ever after being assigned to the Neo-natal Intensive Care Unit, where Weaver and Sandy come needing help with their newly born son, Henry. A case involving a very ill infant tests the souls of all the doctors. Abby does well whereas Neela struggles, but both ultimately decide against going into neo-natology.

The episode was rated 7,78 from 76 votes.

Carter sticks up for Neela when the other attendings doubt her future in the ER. Neela caves to the pressure and accidentally gives a patient the wrong medication without checking medical history. When Neela is confronted, Gallant takes the blame for her. Sam and Luka try to plan Alex's birthday party. Frank visits on his way to therapy. Chen's home nurse quits after her dad behaves poorly.

The episode was rated 7,78 from 78 votes.

Weaver rushes to the aid of her female partner Sandy Lopez when the firefighter is severely injured on the job and must fight for her life. Kerry is devastated when Sandy's family won't let her see Henry. Susan and Risk Management interview everybody who was involved in last week's death. Gallant reveals that the Army is sending him to Iraq and he and Neela share a bittersweet farewell. Sam is surprised by the arrival of Alex's dad. Neela passed her boards, although Abby did not. Corday discovers that she's the new Head of Surgery. After she has contractions, Susan is put on bed rest for the rest of her pregnancy--five weeks.

The episode was rated 7,83 from 81 votes.

Carter is alarmed as he rushes his pregnant girlfriend Kem into the ER when he suspects trouble, but learns the baby died from an unforeseeable accident. Despite his own grief, Carter must help Kem say goodbye to their son after he is stillborn. Nineteen members of Neela's family are coming into town for her graduation. Abby, Neela and Lester graduate from medical school. Steve continues his efforts to get Sam back, visiting Luka at work and sending Sam a box of ice cream sundaes. Pratt refuses to believe that a patient of his is in congestive heart failure. Weaver suggests to Abby that she will match at County, unless she fails her boards. Rachel Greene is in town "looking at colleges," although she has a favor to ask of Corday.

The episode was rated 7,86 from 83 votes.

Romano arranges a meeting with Anspaugh and Weaver to fire Pratt and catches Morris smoking weed in the ambulance bay. A helicopter crashes on the roof, falling into the ambulance bay where it lands on Romano and causes a huge explosion. Susan worries that Chuck was onboard, although it turns out he wasn't, he suffers internal injuries from debris. Abby must intubate and put in a central line without an attending. Luka has Thanksgiving dinner with Sam and her son Alex.

The episode was rated 7,90 from 88 votes.