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.

Carter has a difficult day when he has to identify a dead teenager and notify his parents. It doesn't help that he notifies the wrong family. Doug woos Carol, despite Taglieri's presence in her life. Benton clashes with brother-in-law Walt after he neglects family duties.

A business contractor with a bad heart gathers his family around him in the ER as he prepares for the end. Dr. Ross helps an asthmatic teenage girl when her mother doesn't have the funds. Carter worries that he may have contracted an STD from Liz. Dr. Lewis treats a teenager with alcohol poisoning. Jenn Greene prepares to move to Milwaukee.

Benton and Langworthy interview for the Starzl fellowship. A drunk Chloe throws a tantrum in the hospital. Benton saves a man with a throat wound, earning Morganstern's praise. Carter has a good day, winning a bottle of champagne and getting three leads on apartments. Carol has second thoughts about moving in with Tag after a spontaneous kiss with Doug.

Hathaway treats a rape victim. Walt brings Benton's mother to the ER with a sprained ankle. Carter shows his annoyance toward Benton and his stand-offish attitude. Mark calls in sick to spend time with his wife, leaving Doug as a hectic acting chief. Div shows signs of snapping, overreacting at the smallest provocation. The ER gets a new desk clerk, 'Bob'.

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.

A case of apparent spousal abuse is not what it seems. Deb outshines Carter after he is up all night preparing for a presentation. Peter informs Jackie he's hired a helper for his mother. First Kayson's reprimand against Susan is denied, then Susan has a chance to prove herself when Kayson is brought in as a patient. Dr. Ross meets Diane Leeds, of risk management, and her son Jake.

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.

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.

Kerry Weaver manages to offend just about everyone in her first day as chief resident. Carol goes on a ride-along with paramedics Shep and Raul, sharing a ferris wheel ride with Shep. Peter and Jeanie's secret relationship comes to a head. Susan is stuck caring for Little Susie while Chloe attends school. Dr. Ross has his hands full with a young pyromaniac. Carter shows interest in med student Harper Tracy.

Speculation runs through the ER, on a very hectic day, about Randi's possible criminal history. Mark faces an ethical dilemma when he has to decide whether to report yet another of Doug Ross's indiscretions--Doug slept with med student Harper Tracy. Carter becomes upset when Harper confesses this to him. Carol meets with a mobile notary to finish the paperwork to purchase a house. Bernstein informs Doug that he need to look for other employment. Benton is visibly upset when Jeanie begins work in the ER as a physician's assistant.

In the middle of a torrential rainstorm, Dr. Ross stumbles across a child trapped in a drainage pipe rapidly filling with water. Doug does everything possible to save the boy, Ben Larkin. Harper develops a bond with a young girl with separated parents.

Doug's heroics earn him a second chance as Bernstein and Morganstern ask him to stay on. Doug and Mark clash when each treats a seriously injured patient and want to use the same equipment. Benton learns that Jeanie has separated from Al. After missing an earlier diagnosis, Carter overcompensates on his next patient and catches a break when the test results reveal something. Shep gets on Carol's bad side when he makes disparaging remarks about the people who make botched suicide attempts. Doug gets a phone call from his estranged father.

Carol and Jeanie try to find a home for a schizophrenic architect. Carter signs Benton up for an interview with Vucelich for a prestigious study. Carter and Harper try to find a place to make out. Jenn and Rachel are involved in a car accident; Mark is thrown for a loop when he learns that Jenn has been having an affair with a coworker. Doug dines with his mother. Susan receives $3000 in the mail from Chloe.

The ER staffers are in decidedly unfestive moods as Christmas arrives. Carol's spirits are lifted by a Santa-like patient. Mark is outraged when Jenn decides to stay in Milwaukee over Christmas. Benton and Carter score points with Vucelich when Carter convinces an older gentleman, Ruby, to include his wife in Vucelich's study. Mark gives a deposition in the O'Brien case. The death of a priest threatens to start a gang war. Weaver receives a surprise visit from an African friend. A Holocaust survivor, the victim of a carjacking, brings Chanukah to the ER.

Mark tries to find a way to tell Rachel about his impending divorce. Benton attends a banquet at Vucelich's home, with Jeanie as his date. Carter finally tells Mr. Rubadoux about his wife's terminal condition, making the man furious. Morganstern is admitted to the hospital after breaking a leg at a Scottish family reunion.

Mark is riddled with self doubt as the hospital prepares to settle the O'Brien suit. Kerry appoints herself as Susan's personal mentor. Carol mind a bucketful of expensive worms. Doug balks at counseling a teenage boy who thinks he might be gay. Benton uncovers some disturbing information concerning Vucelich's study. Carter steals a diagnosis from Harper.

Mark finds himself manning a very crowded ER on his scheduled night off, filling in while Doug is out with whiplash and Susan meets with her lawyer. He tries to juggle hunger pangs, 40+ patients in the waiting room and a never-ending stream of traumas.

Susan throws herself into her work to escape her stressful personal life, earning recognition from Kerry and Mark, who begins preliminary discussions on next year's chief resident. Carter needs a pedes rotation, and fast, with Doug to graduate med school. Doug takes up with his father's girlfriend. Shep overreacts and attacks an Asian boy interfering at a scene. Mark and Jenn try to discuss their divorce amicably, with unforeseen results. Benton is named Resident of the Year. Harper leaves for an OB rotation at Parkland in Dallas.

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.

While the whole staff is worried the ER might close, Jeanie has her own problems in dealing with being HIV-positive.

Encouraged by Carol, Mark finally asks Susan out. Benton tries to save a boy, despite the fact Doug thinks he's brain dead.

Carol worries about her physics exam while Mark is heart-broken about Susan's departure and focuses solely on his job.

Benton can't keep his mind on the job, Mark and Chuny break up and Carol does what she needs to do regarding the fatal error she has made.

While a film crew is filming in the ER, it's Elizabeth Corday's first day.

Carter is exited about getting his own med student and Mark and Carol interview candidates for the desk clerk position.

Jeanie fears Scott Anspaugh's cancer may have returned. Hathaway learns a disturbing secret about a 16-year-old girl. A pregnant patient fears she'll miscarry; Morgenstern returns to work, but perhaps too soon after his heart attack.

Carter finally works up enough nerve to ask Del Amico out. Jeanie tries to help Scotty decide whether to undergo an experimental treatment and Benton takes unexpected action during an operation with Morgenstern.

Del Amico, Ross and Corday confront disturbing situations after the bombing of a women's clinic. Benton comes under review for controversial actions in the OR. Jeanie endures one of the most difficult days of her life as she says goodbye to a friend.