Dr. Lewis tries to get a mentally disturbed individual admitted to the psych ward. Carter has a difficult day, treating many members of wedding party, suffering from food poisoning. Dr. Ross finally visits Carol, eight weeks after her suicide attempt. Dr. Greene deals with an elderly gentleman having a difficult time letting go of his dying wife. He also discovers that Jenn passed the bar exam.

Morganstern invites Mark to join the staff as an attending physician. Mark treats an woman with breast cancer, who begs him to kill her. Deb "wows" Benton with her amazing presentation, leaving Carter in the rear again. Benton offends Haleh, who spends her day making his job extremely more difficult. The ER gets new crash carts, which are promptly stolen by cardiology.

Peter refuses to sleep, despite Hicks' order, in the middle of a 48-hour shift. His lack of sleep catches up with him when he is supposed to be watching his mother. A doctor, who turns out to be a con artist, visits the ER to use it as a model for a new hospital, in the process offering Susan a job. Jenn tells Mark she wants to separate from him. Dr. Ross treats an abused young girl. Carol receives bad news about her attempt to adopt Tatiana. Morganstern informs Mark he's leaving for Boston and will be strongly recommending Mark to his replacement, leaving a surprised Mark uncertain as to his job prospects.

Carter faces his last day in the hospital with aplomb, harshly grading Benton on an evaluation report. He later rescinds the report after finding out that the surgical sub-I is his. Carol faces wedding day jitters, culminating in Tag's deciding to call off the wedding. Chloe disappears again, abandoning little Susie with Susan. Dr. Swift changes his mind and decides to support Mark. Jake visits Doug.

The ER treats victims of a gang shootout. Carter arrives late and unprepared for his new position. Mark learns all about being an attending, including senior staff's habit of bad-mouthing the residents, particularly Doug Ross. Mark hires a new chief resident, Kerry Weaver. New third year med students arrive to complete their ER rotation.

Shep and Raul bring a dozen malnourished and abandoned children into the ER, keeping everyone very busy. Shep has a run-in with Malik and Benton when he makes an off-handed racially insensitive remark. Carter's high from the admission of Mrs. Rubadoux to the study ends when she shows no signs of recovery. Jeanie and Carol clash when Jeanie receives a poor evaluation. Al asks Jeanie to give him another chance. Mark is served with divorce papers.

Shep and Raul respond to a massive fire without proper equipment, risking their lives to save addicts and their children. Shep will be okay, but Raul has third-degree burns covering his body; it's only a matter of time. The ER is flooded with burn victims. Chloe returns to Chicago. Doug is stood up by his father for a basketball game.

Carol is pushed to the breaking point after another day when politics triumph over health care, and she quits. Dr. Greene "trades his soul" when he agrees to back Weaver for ER attending, in exchange for her support of Susan for chief resident. Jeanie takes an HIV test and informs Peter he should get himself tested as well. Carter invites Benton to his med school graduation, which he himself misses. Shep's refusal to see a psychiatrist risks his relationship with Carol.

It's the first day of Carter's internship. He has a 36 hour shift and overnight he has to cover the ER, the ICU as well as the surgical patients.

Carol will hear whether her suspension is permanent or not. Mark and Doyle do what they can to get a patient with Down syndrome on a heart transplant list.

Anspaugh is furious when Carter tells him he wants to quit surgery. Charlie is brought in with an overdose. Mark keeps struggling with his beating.

Ross and Greene travel to a near-deserted stretch of California to investigate circumstances surrounding a death in Doug's family.

Another elderly rape victim is brought in. So is the rapist.

Doug faces possible criminal charges after Ricky Abbott dies when Ross bypasses system lockouts to enable Joi to give Ricky a lethal dosage of dilaudin. Doug is delegated to desk duty, Carol's clinic is shut down for acquiring the P.C.A. machine for Ricky, and Greene and Weaver face future disciplinary action for not reporting Doug's tampering with the double blind study. Carter and Lucy discover a mutual attraction. Benton studies with a sign language instructor.

Greene assists paramedics in treating injured children at a school bus accident. En route, Doug and Jeanie survive their own accident. Kerry stops Doug from treating Jeanie...or any other patient. Doug decides to resign and leave Chicago for the Northwest and asks Carol to come with him. She decides against it, but he leaves anyway. Carol steps down from running the clinic so that Anspaugh will keep it open. Jeanie discovers she may have contracted hepatitis. Hospital janitor Mobalage's wife is stabbed.

Benton struggles with the idea of taking a DNA test to determine whether or not Reese is actually his son. As the signs continue to pile up, Kerry and Mark use a fake patient to convince Dr. Lawrence of his Alzheimer's. Carter has trouble persuading a woman from a nursing home fire to sign a DNR for her husband and later is asked to forge charts for a family with no insurance. Carol continues to meddle in Meg's life, having her arrested so that she can be detoxed. Cleo is blamed for an explosion in the suture room but it may actually be Dr. Dave's fault.

Greene prepares to bury his father. Chen worries about Carter's mood swings. After witnessing the interaction between a dying woman and her family, Hathaway realizes she wants her family together and flies to Seattle to join Ross.

Corday rushes through a surgical procedure in order to take off on a romantic weekend with Greene. She is later called back to the hospital after her patient suffers complications. Abby's mother, Maggie, who suffers from bipolar disorder (manic-depressive) and refuses to take her medication, unexpectedly visits Abby at the hospital and wreaks havoc on Abby's life.

As the new director of diversity, Benton studies medical school applications and discovers that his own academic record did not qualify him--he was admitted because of affirmative action. Weaver feels uncomfortable amongst Legaspi's lesbian friends. Carter treats an unvaccinated child who contracted measles.

After some staff members are caught going through a dominatrix's bag, Weaver makes them attend a sexual harassment seminar, where they learn about each other.

Dr. Greene's final days are spent in Hawaii with Rachel, teaching her to drive and surf. When he suffers a seizure, Elizabeth is called. Mark refuses to go home. He manages to make amends with his daughter before his eventual death.

Carter travels to the Congo after Luka calls and asks for help. During the course of his two weeks there, he learns how much different the conditions are against what he's used to. Luka decides to stay for a while as Carter heads back to Chicago, ending up at a sleeping Abby's bedside.

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. 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.

John Carter returns to the Congo to retrieve Luka Kovac's body. He finds however that the area where was killed is still too dangerous to enter. He and Gillian finally manage to hitch a ride with a Red Cross worker, Debbie, who is going to the area. In flashbacks, we learn how Kovac and his fellow aid workers were taken prisoner by rebel troops. They are shot, one at a time, until only Luka is left. Amid the destruction of the eastern Congo, we learn his fate. Carter also makes a fateful decision.

Dr. Carter celebrates Christmas at a clinic in the Congo dealing with low supplies and anti-Americanism, but in the meantime, falling for an AIDS worker named Makemba.

Carter takes Kem to the hospital to check on their baby since it's not kicking anymore.

After Carter finds out Kem's mother is hospitalized in Paris he decides to go there to tell Kem how he feels about her. Meanwhile, Ray makes a fatal error.

Sam and Luka go on the search for her runaway son, Alex. Meanwhile, Pratt and Lewis guide Abby, Neela and Ray, who have become R2's, on how to teach the new interns.

Neela and Sam are shocked when they arrive back to the airport with transplant organs only to find that their plane has left them. Dr. Carter gets a surprise visit from an old friend while waiting for his kidney transplant. Dr. Banfield bonds with an abandoned baby boy that is left at the ER.

As Carter prepares to open a new facility for the underprivileged, some old friends/colleagues gather. Rachel Greene, Mark Greene's daughter, applies for an internship at County.