A belligerent young man who claims to have the flu turns out to be more than he seems, and presents a challenge to Morris and Sam when he refuses treatment. Abby's chance encounter with Curtis Ames leaves Kovac uneasy. Meanwhile, Pratt discovers a local church's risky drug exchange program, Neela and Gates square off, and Weaver gets an interesting offer.

Thanksgiving at County is quiet, with the normal number of routine (or nearly so) emergencies. But Abby makes up for the lack of excitement while returning to the hospital as the doctor on a helicopter transport.

Kovac and Gates treat a girl who appears to have been assaulted. When the police are no help with Ames, Kovac decides to confront the problem himself; Morris and other doctors work on a patient with an ice pick in his ear. Meanwhile, Ray tries to keep his new relationship a secret and Pratt can't fully deal when his half-brother officially comes out. Also, a new male nurse arrives.

It's Christmas in the ER. A homeless boy sends Gates and Ray on a mission. Meanwhile, in the ER, Neela oversees an unusual kidney transplant case; Sam takes a stand when a patient is dumped in an alley by another hospital; and Morris plays Santa for a special girl and learns the meaning of Christmas.

Kovac finds himself in a tense confrontation with Curtis Ames, and Abby must act to protect her family. Meanwhile, Neela and Gates rush to get Meg to the hospital while Sam's new home is soon under threat from fire.

Kovac and Gates deal with a hopeless father whose son succumbs to heart failure; Pratt tries to resolve the tension between him and his brother; an Armenian man tries to be a good samaritan but ends up crashing near the ER; Abby sneaks in baby Joe when she worries his sickness may be worse than it seems; Also, Sam injures the instructor of a self-defense seminar.

What is supposed to be a departmental dinner organized by Kovac turns out to be the surprise of a lifetime for Abby when she learns it's a surprise wedding, secretly planned by the eager groom. Meanwhile, at the wedding, ER staffers enjoy themselves with music and booze while Neela finds herself the center of unexpected attention between Gates and Ray, which leads to a drunken fight and a shocking conclusion.

The ER reopens with new changes. However, the ER is not the only thing that's changed; Kovac and Abby adjust to being newlyweds; Morris and Hope enjoy themselves at the honeymoon suite; Pratt attempts a change for a woman; Neela worries when Ray goes missing; Meanwhile, there's a new doctor in the ER and he means business; and another change may come when Kovac receives a phone call.

The ER is now in the hands of a new chief, Dr. Kevin Moretti, who is bent on major changes. Meanwhile, a phone call leads Neela to a hospital where a major shock awaits her, and a final farewell from a friend and colleague. Gates urgently goes home to stop Sarah from being taken away from him. A drug-addicted Iraq War veteran baffles Morris and Sam. Also, Kovac postpones the honeymoon and says goodbye to Abby and his son, for the meantime, while he travels to Croatia to visit his ailing father.

Abby and a distracted Morris work to save two auxiliary cops brought in with gunshot wounds. Pratt treats a teen wrestler with severe vomiting, but the problem is much more serious. Sam worries over her new beau Litchman. Gates tries to help a young boy in the ICU with a deadly disease. Also, Dubenko visits Neela while she babysits baby Joe.

When Baby Joe is injured by a fall at the playground and rushed to the hospital, Abby is unable to reach Luka to tell him.

Moretti reassigns Gates back to the ER and treats a couple involved in a car accident. Morris prepares to take his written board exams. Neela is assigned a young genius intern. Kovac plans to extend his stay in Croatia while Abby struggles with single parenthood.

The city suffers power outages during an unseasonably hot spell. Nursing-home patients are brought into the ER suffering from hyperthermia. Abby and Pratt disagree on the diagnosis of a fussy baby. Abby falls back to old habits and quickly spirals down to rock bottom on a night she'll forever regret.

Gates and Julia nurture their newfound romance but are soon interrupted by a troubled phone call from Gates' ward, Sarah.

Dr Wexlar is made interim ER chief while staff deals with an industrial accident that leads to a hate crime.

Morning shift begins. The night shift treated 142 patients - a new record. Dr. Morris is confident that by the end of the day the ER can set a new record of 300 patients. Frank reminds him that there has never been more than 250 patients in a day. Dr. Morris bets $300 that they can reach 300 by the end of the shift. Frank, Dr. Gates and Dr. Pratt each bet $100 against him. But will the game be fair? Also, when chaplain Dupree arrives announcing that she's doing a round of the hospital, holding blessing ceremonies and memorials, the guys are against it, except for Dr. Gates, which makes the others suspicious. Frank goes straight to the point. Then there is the accident involving a camel.

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.

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.

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.

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