A day's worth of trauma takes its toll on the men and women of the ER. Dr. Greene looks into leaving the ER and joining private practice. Among other events, multiple casualties are brought in when a building collapses. New medical students report for duty, including Dr. Benton's new trainee, the young and inexperienced John Carter.

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.

Carol returns after her eight week absence, finding Doug holding himself responsible. Carter finds himself watching over a mysterious, mentally ill singing woman. Susan clashes with Dr. Kayson over a diagnosis. Dr. Greene treats a domestic violence victim.

A severe blizzard leaves the ER utterly devoid of patients, leaving the staff free to goof off. In the middle of their fun, a call comes from dispatch, informing the ER of a 40-car pile-up with dozens of casualties. The ER goes from being deserted to capacity. All surgeons are called in. Bob surprises everyone with a quick and life-saving decision. A new doctor, Angela Hicks, arrives just at the right time. Ross and Linda return from the Caribbean just as Carol makes a surprise announcement.

Benton makes a critical error when he publicizes the availability of a dying man's organs before obtaining the wife's permission. Lewis discovers that Cvetic has quit his job at the hospital, moved out of his apartment, and dropped out of sight. Carter makes a move on Susan. Chloe announces her pregnancy.

Carter fumbles his way through his first look at surgery. Dr. Lewis' nemesis, Dr. Kayson, makes her New Year's Day decidedly unpleasant. Chloe announces she's moving to Texas with her boyfriend.

Carter trains one of Benton's new students, Deb Chen. Hathaway has her hands full with an emotionally challenged patient who's obsessed with colors. A sociologist provokes people to measure their reaction times for a study. Kayson brings charges against Susan in the Vennerbeck death, leading Morganstern to question Susan's assertiveness. Benton and Walt hunt for Peter's missing mother.

Gates is assigned to the case of a closeted gay man whose partner clashes with his family; Neela meets her new surgical chief, Dr. Crenshaw; and Pratt must cope with the flood of new interns.

Abby and Kovac discover both the joys and difficulties of raising a newborn; Morris is wrongfully accused of being a child molester; Pratt has his trial-by-fire when he has to handle the ER alone, juggling multiple traumas, teaching duties and a troublesome intern. Neela continues to be the target of her difficult supervisor, and Sam discovers her sons latest extra-curricular activity.

Curtis Ames, a carpenter who suffered a stroke under Kovac's care, sues him for malpractice. Kovac and Ames square off in court as each man's recollections of Ames' treatment are recounted via testimony and flashbacks. Meanwhile, Abby returns to work and must adjust to the dramatic changes in her life, and Pratt's early morning trip to the barbershop results in a new awareness of community need. Also, Abby and Pratt try an unconventional method for treating a heart patient and Neela tries a risky procedure which doesn't sit well with her chief.

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.

Weaver cares for a Katrina survivor who's reluctant to having surgery on her foot; budget cuts force Luka to make a difficult personnel decision. Also, Gates' home life intrudes on the ER; and Pratt and Hope are shaken after a patient in their care dies needlessly.

Kovac reacts negatively when he sees Abby giving extra attention to a patient; Ray and Gates clash over a patient, pinning Neela in the middle; and Ben takes things to the next level with Sam. Meanwhile, Pratt is under investigation and Weaver says a final goodbye to the ER.

Abby and Sam try to treat an obnoxious, aspiring comedian with mysterious symptoms; Pratt must defend his actions in front of the medical board; Neela scrubs in on a kidney donor transplant; and Morris, as the lone attending, must run a busy ER. Also, Kovac gets a surprising proposal from Abby.

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.

In 12 hours, the ER will shut down. As Kovac is under pressure to take care of the patients before the final hours, he makes a pivotal decision about his future. Meanwhile, Sam befriends a photojournalist who returns only this time she's terminally ill; Pratt is concerned when his brother ends up in the ER drunk; Morris confronts Gates when he ignores his orders and angrily sends him home while Gates tries to defend his actions.

What is suppose to be a departmental dinner organized by Kovac turns out to be the surprise of a lifetime for Abby when she soon 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.