Abby deals with her upcoming reunion with Luka in Croatia, a heart transplant patient is admitted when her body rejects the new heart, and a new doctor ruffles feathers.

Abby returns to work; Luka applies for a job elsewhere; the reason behind a brash doctor's being at County is revealed.

A young couple is choppered to County after a car accident, and one of them has a gun. A boy who wants to be a clown is injured in a unicycle mishap, but his father considers him a mathlete and wants him to go to MIT. Pratt visits Bettina in the hospital, but she tells him off.

A young woman with a failing liver has a difficult reunion with her parents, whom she has not seen in six years. Abby receives a job offer. Brenner isn't nice to Laverne after they sleep together.

In the season finale, an ER patient with a mysterious past is afraid that people are trying to kill him. Dr. Moretti returns, trying to make amends for wrecking the marriage of Abby and Luka. Neela makes her way through a difficult M&M conference. Morris treats a woman with lupus who has an attractive daughter.

The ER staff deals with the aftermath of the explosion including a severely injured doctor.

The ER is on guard as Gates gathers the new interns to treat a terrorist, but it's the new doctor and her tough disposition that has everyone on the defensive.

When a gunshot wound victim arrives, the new chief and Abby butt heads on how to treat the patient. Abby comes to Sam's defense when she goes before a nurses disciplinary board.

When a thirteen-year-old gymnast is brought into the hospital after having supposedly fallen off a wall, Dr. Banfield and Dr. Gates must sort out whether abuse is involved.

Patients include an 18-year-old who was stabbed with a fork at his school, and a man shot by a cop at a Halloween party. Meanwhile Sam is annoyed by Gates and Daria.

Both Morris and Neela have authority issues with Dr. Banfield and Gates upsets Sam.

Trying to rescue a three-year-old girl from drowning in a nearby lake, Banfield is reminded of her own experience at County with Dr. Greene caring for her son.

A woman who broke her leg while trying to escape a house fire is brought in with her husband. The husband, Mr. Lotery did not let the paramedics to check him over. Then his brother-in-law arrives, saying that he predicted that something like the house fire would happen - it was actually an arson. Mr. Lotery's brother-in-law becomes aggressive and accuses him of being a pervert, specifically a pedophile. Mr. Lotery denies the accusations. He was sued but found not guilty. When Mr. Lotery is waiting for his wife who's in line for X-ray, he has the chance to calm down a young girl who is afraid of needles. When his brother-in-law sees this, he brutally assaults him, while Dr. Brenner calmly watches nearby... Meanwhile, Neela gets sued for malpractice.

As a snowstorm hits Chicago, Sam's son Alex crashes a car and ends up in critical condition in the ER. Neela gives a deposition in the malpractice suit against her. Dr. Morris and Dr. Banfield are both at a medical conference in Omaha, and when the snow cancels all flights out they share a memorable and surprising evening.

The Last One Before Christmas Break. The one in which Frank and Drs. Sanchez and Wade accidentally get brownies with cannabis in it. The one with the Christmas party. Archie's cousin brings Archie's deceased father's storage container to the ER bay. An injured pregnant Latino woman is brought in. There is something wrong with her baby?. Plus, the Immigration Office wants to deport her.

The police wheel in a casualty of a drug deal-turned-shoot-out. They also bring in an injured woman who was the shooter, plus a pair of wounded brothers who were shot by the man who was shot dead. A 13-year old girl with sickle cell disease is brought in because of abdominal pains; Neela takes her case while Tracy learns from her. Banfield's pregnancy test is negative, which leads to a discussion with her husband and a visit to a specialist.

Neela experiences alternate versions of the same day.

A girl who was hit by a car while riding a bicycle is treated in the ER. When her boyfriend turns up, it seems it may not have been an accident. While a lottery has made millionaires of several nearby convenience store workers, Dr. Banfield and her husband are at the fertilization clinic hoping for their one in a million chance. And as an older woman is brought in assisted by her on-again, off-again husband, three love stories continue in the ER: Dr. Morris meets policewoman Diaz again, Sam discovers that Tony has been seeing Daria, and Neela plays it cool with the returning Dr. Brenner.

An elderly man is brought into the ER after being mugged, and sees things as if it were the 1960s.

A single mother is hurt in a car accident, and must find someone to take care of her daughter. Gates treats a 78-year-old man who refuses surgery that would save his life. Meanwhile Morris's afternoon date with Claudia is not what he expected.

Dr. Carter returns to Chicago and talks Dr. Banfield into allowing him to pick up a number of shifts (without pay). Other happenings include Banfield's dogged pursuit of motherhood, Neela's intensifying personal relationship, and Archie's involvement with a patient who was probably beaten while in police custody - with his new girlfriend the detective standing by.

Banfield and her husband look into adoption, while Carter adjusts to a changed ER. Sam's mother comes into the ER in an altered state of mind.

Carter's illness overtakes him during a critical procedure in a trauma room as a documentary film crew spends the day interviewing the health care givers.

A girl drops off a sick baby at the ER and then leaves; Carter may get a kidney transplant; Gates and Daria care for an elderly woman with multiple sclerosis; Neela and Sam are in Seattle to transport a heart for Joanie Moore, while Doug and Carol are concerned that the donor's grandmother might not consent.

On Neela's last day at County, she has doubts as to whether she is making the right decision.

The ER doctors and nurses help out at Camp Del Corazon, a camp for kids who have had open-heart surgery, working alongside the camp counselor.

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.

A woman who broke her leg while trying to escape a house fire is brought in with her husband. The husband, Mr. Lotery did not let the paramedics to check him over. Then his brother-in-law arrives, saying that he predicted that something like the house fire would happen - it was actually an arson. Mr. Lotery's brother-in-law becomes aggressive and accuses him of being a pervert, specifically a pedophile. Mr. Lotery denies the accusations. He was sued but found not guilty. When Mr. Lotery is waiting for his wife who's in line for X-ray, he has the chance to calm down a young girl who is afraid of needles. When his brother-in-law sees this, he brutally assaults him, while Dr. Brenner calmly watches nearby... Meanwhile, Neela gets sued for malpractice.

A single mother is hurt in a car accident, and must find someone to take care of her daughter. Gates treats a 78-year-old man who refuses surgery that would save his life. Meanwhile Morris's afternoon date with Claudia is not what he expected.

An elderly man is brought into the ER after being mugged, and sees things as if it were the 1960s.

Abby deals with her upcoming reunion with Luka in Croatia, a heart transplant patient is admitted when her body rejects the new heart, and a new doctor ruffles feathers.

The ER doctors and nurses help out at Camp Del Corazon, a camp for kids who have had open-heart surgery, working alongside the camp counselor.

The ER staff deals with the aftermath of the explosion including a severely injured doctor.

Banfield and her husband look into adoption, while Carter adjusts to a changed ER. Sam's mother comes into the ER in an altered state of mind.

Dr. Carter returns to Chicago and talks Dr. Banfield into allowing him to pick up a number of shifts (without pay). Other happenings include Banfield's dogged pursuit of motherhood, Neela's intensifying personal relationship, and Archie's involvement with a patient who was probably beaten while in police custody - with his new girlfriend the detective standing by.

A girl who was hit by a car while riding a bicycle is treated in the ER. When her boyfriend turns up, it seems it may not have been an accident. While a lottery has made millionaires of several nearby convenience store workers, Dr. Banfield and her husband are at the fertilization clinic hoping for their one in a million chance. And as an older woman is brought in assisted by her on-again, off-again husband, three love stories continue in the ER: Dr. Morris meets policewoman Diaz again, Sam discovers that Tony has been seeing Daria, and Neela plays it cool with the returning Dr. Brenner.