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 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.

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.

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.

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.

Dr. Corday begins her first day as an intern, first by being assigned to Dale Edson, then being treated as Romano's lapdog. Kerry is interviewed for ER chief. Doug and Carol ponder parenthood when Carol realizes she may be pregnant. Carol and Lynette try to keep a wounded gang-banger from leaving and seeking retaliation. Lucy faces the wrath of Carter when he discovers that she doesn't know how to start an IV. Jeanie asks Doug if she can be a full-time PA for the pediatric ER.

Dr. Corday commits a deadly error after being on-call for nearly 36 hours straight. Peter visits Dr. Kotlowitz and receives encouragement regarding a cochlear implant for Reese. Dr. Amanda Lee, a prospective new ER chief, visits. In the wake of a failed pregnancy attempt, Carol lashes out at a mother using abortion as a means of selective birth control. Carter and Lucy feud when Carter accidentally uses her palm computer and finds out what she thinks of him. Mark panics during a paramedic initation.

Carter plays tour guide for Ruth Johnson, who was born in the hospital 100 years ago to the day, and her large family. Carol treats a boy who was hit by a car and tells a story of being chased, his friend being shot in the process. Peter observes Kotlowitz install a cochlear implant and decides to wait before scheduling an operation for Reese. Mark dines with Dr. Lee, new ER chief. Dr. Corday proposes radical changes in scheduling at an M&M conference, and later decides to break off her relationship with Benton.

When Anspaugh decides to retire as chief of staff and return to surgery, he appoints Romano as his replacement. Greene expresses reservations about the decision, but Weaver does not support Greene. Romano makes Weaver the new chief of emergency medicine.

Mark Green is in New York on New Years Eve for cancer surgery. Meanwhile a father and son are involved in a car crash.

After another hospital shuts down, the ER is flooded with patients. Dr. Pratt resuscitates a heart-attack victim who had been pronounced dead.

Weaver makes a mistake on live television while demonstrating flu shots, inadvertently sticking two reporters with the same needle. In the bathroom later, Susan and Abby catch Weaver in a stall with a needle. Weaver confesses to Susan that she's taking hormones. Carter, assuming Susan knows already, tells her about Abby's drinking problem. Abby becomes nurse manager, and argues with Carter about her drinking. Luka flirts with a patient's mom and is caught emerging from a storage closet with her. Gallant has a rough day: Pratt butts in on a patient of his, and Stella Willis dies because Kayson didn't bother with thorough treatment.

Dr. Pratt brings a gun into the ER; Dr. Weaver tries to conceal her pregnancy; a woman plots against her dying husband; Dr. Chen treats math students who overdosed on an unknown stimulant.

Morris streets a patient without getting a psych consult, and the guy steals a tank and heads for County. Gillian is visiting Luka, and Sam's not happy about it. Luka and Sam make up by the end of the day though. A 13-year-old boy has chlamydia. Frank has a heart attack. Corday plays the dating game, going out with two men.

Carter, Pratt, Kovac and Abby are dealing with a woman and her three children who've jumped from a three floor apartment trying to escape from the father. Meanwhile Dr. Lewis becomes Chief of Emergency Medicine, Howard quits his internship and Dr. Corday is facing dismissal.

Jules 'Ruby' Rubadoux is back in the ER. He's still angry with Carter about the death of his wife.