Greene and Weaver agree to go out on a limb to oppose Romano's appointment as chief of staff. However, soon Greene finds he is out there alone, while Weaver reaps immediate benefits for her treachery. Luka Kovač, an able, yet untrusted, physician from Croatia, arrives at the ER for his first day of work. Carter's interested in a romance with his cousin's ex-wife. Hathaway adjusts to being pregnant alone.

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NOTE: First appearances of Dr. Luka Kovač and Dr. Cleo Finch

Who's the boss? Weaver may be head of the ER, but Greene has his own ideas about how to handle situations and after his mother's death the two of them have their worst conflict on the job yet. Boulet says "yes" to Reggie, and Corday accepts Romano's surprise job offer. A brash new resident, Dave Malucci, arrives and manages to annoy just about everyone. Carla confronts Benton about not allowing her to leave the country with their son. Carter and Elaine's relationship continues.

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NOTE: First appearance of Dr. Dave Malucci

The newly appointed attending physician (guest Alan Alda) is savvy, personable and, in Greene's jealous opinion, unsuitable for County. Jeanie and Reggie marry, but not under the circumstances they expected. Romano makes Corday show a rude reporter around the ER, where she witnesses a shootout. Carter tries to be supportive as Elaine undergoes her mastectomy. Corday and Romano are staggered by the front-page hatchet job the rude reporter publishes---she's offended by the reporter's misinterpretation but Romano is offended because it didn't trumpet him. Greene and Corday spend their first night together.

Greene deals with the fallout from his dad's car accident. Lawrence suspects a teen's suicide attempt is the fallout from father-son strife, but he is wrong. Finch misdiagnoses a little girl's behavior before an iron overdose has the staff battling to save the little girl although they are unsuccessful. Hathaway tries to help a pregnant woman get a job at the hospital, and Dr. Dave Malucci is a jerk again. Carter makes plans to meet with Elaine.

A high school science experiment/prank gone-wrong lands students and teachers in the ER - and the stress of multiple emergencies pushes Lawrence over the edge. Greene defends a patient from a violent parent and ends up being castigated for it. Lucy helps counsel one of the injured students. Hathaway learns the pregnant woman she wanted to help is using drugs. Elaine tells Carter that she intends to go to Europe for a couple of months asking him not to contact her.

Boulet resigns to be a full-time mother. An elderly woman bids farewell to her dying husband, and Lawrence admits he is in the early stages of Alzheimer's, and that his distinguished career is over. Hathaway takes action regarding the pregnant drug-addict case. An explosion rocks the ER, and Benton tells Carla why he is fighting to stay in his son's life.

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NOTE: Final regular appearance of Physician Assistant Jeanie Boulet.

Lawrence departs (but not before saving a life), and Kovač comes aboard full time after earning Weaver's respect. Corday discovers her new trauma patient is a rapist and takes extreme measures to find his latest victim. Hathaway and the formerly pregnant drug-using woman have a confrontation. Carter angles for more responsibility inside the ER. Greene's father was due to fly into Chicago but shows up hours after his scheduled arrival time. And the Bright Star Gospel Choir is rushed to the ER.

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NOTE: Final appearance of Attending Physician Gabriel Lawrence.

It is Thanksgiving, and Hathaway has two more reasons to give thanks after overcoming complications and delivering twins Tess and Kate. Greene's family celebration comes with its own complications. Malucci stuns the staff by actually having a valid idea to treat a patient that works.

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NOTE: First appearance of Nurse Abby Lockhart

Lucy risks Romano's wrath (and her career) to arrange a heart operation for a patient. Corday is conflicted when the rapist from earlier is arrested on other charges and then develops a potentially fatal clot issue, leaving her to consider whether to convince him to have life-saving surgery or just let him die. Carter gives gifts to inner city kids in exchange for their guns. Finch uses her authority to put a teen binge drinker into rehab. Benton and Carla's custody battle comes to an abrupt end that works out in his favor. Weaver befriends a group of Santas and works on County's Y2K preparation.

Deb Chen returns to the ER as Jing-Mei Chen and immediately shows off her great photographic memory to Carter's annoyance. Kovač's strong sense of family involves him in the fate of brothers facing separation. Greene invites his lonely dad to reside with him in Chicago. Malucci fixes Weaver's car and learns a young patient has a fatal disease. Goofball students arrive in the ER to do a scavenger hunt. Benton does not agree with Cleo's approach to an overstressed young high school athlete. Corday takes an extreme measure to help the police and a family whose missing daughter was killed by the rapist.

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NOTE: Dr. Jing-Mei "Deb" Chen returns to the show after having been a recurring guest star in Season 1.

A precious donor heart becomes available when a patient who recently received it dies, devastating Lucy. Malucci gathers evidence to shut down a backroom clinic. Carter and Chen disagree on when to follow rules and when to break them. Greene learns a man is being abused by his boyfriend. A water shortage leaves the ER doctors finding creative ways to treat patients. Corday lets the rapist know he has no hold over her anymore.

Abby Lockhart, the part-time OB nurse who cared for Hathaway during "Great Expectations", reports to the ER for her third-year med-student rotation. Hathaway has a hunch that a young patient's health problems come from his mother. Carter and Cleo try to help a sick boy and the unpopular student he fought with. Weaver leaves the ER due to the flu, while Malucci works in spite of it and Benton angles Romano's illness into some help for a young girl who was mauled by a dog.

It's a usual Valentine's Day in the ER with the couples making holiday plans, while an unusual case involves Corday assisting Romano operating on his own dog. Benton, Corday, Kovac, and Hathaway work on a family of four, and are unable to save the parents, leaving the children orphaned. Greene wrestles with Chen and Malucci as they bicker over a patient in their care. Carter helps Lockhart with an elderly patient, while ignoring the warnings of Lucy, who becomes suspicious of her patient, Paul Sobriki (David Krumholtz), and his deteriorating mental state, the end result bringing disastrous consequences as he attacks both of them.

The ER's Valentine's Day activities ends abruptly when Dr. Weaver discovers Carter and Lucy lying unconscious on the floor of Curtain Area 3, suffering from multiple stab wounds each, with Lucy worse off. The staff work valiantly to save their colleagues. Benton and Anspaugh repair the damage to Carter while in another operating room, Corday and Romano fail to save Lucy. Later, the psychotic patient who attacked them arrives back in the ER after an accident and things take a dramatic turn for the staff, which becomes even more so when the patient's wife arrives looking for her husband.

NOTE: Final appearance of medical student Lucy Knight

A child is injured in a hit and run in front of Kovač (the driver later turns up in the ER), and a teen has cervical cancer after becoming infected with HPV. Lucy's mother comes to retrieve her property---and surprises a still-struggling Carter with her late daughter's gratitude and praises for his guidance with her. The encounter succumbing the recovering Carter into a depression. Even a happy event, a romance between Corday's mother Isabelle and David Greene, turns sad when Greene learns his dad is terminally ill.

"We can handle this." This, it turns out, involves a Gila monster, toxic breast milk, a deadly error and much more as Greene oversees a particularly hectic shift. Carter, despite his pain, returns to work. Chen is attracted to a very handsome male nurse.

Kovač and Corday must select a recipient while a donor kidney is still viable, and Kovac's moralistic/judgmental side doesn't impress Corday or settle the argument in his favor. Weaver defies Romano on treating a poorly-insured patient and is suspended. Benton's careless penmanship results in a patient taking the wrong drug, and he blames Finch when the patient ends up in the ER having suffered a heart attack. Chen wants to tell the daughter of a patient about her father's diagnosis of Huntington's disease but Greene puts the brakes on that. Greene has his own conflict with both his father and Corday over David's desire to check into a hospice care center.

A notice of Lucy's acceptance into psych residency deepens Carter's depression and guilty conscience. Greene cares for his father's deteriorating health. Hathaway has news from Ross. Abby convinces an overwhelmed mother against the wishes of her controlling and unhelpful (but devout) husband with getting an abortion. Kovac helps out a bitter divorced father who is facing a horrible diagnosis.

Memories. After his father reminisces about his Navy days, Greene takes him on a final boat ride on Lake Michigan. Meanwhile, Carter is haunted by terrifying thoughts of the attack that almost killed him, and has a cordial but inconclusive talk with Paul Sobriki's wife. Kovač helps Hathaway buy a used car, before describing what happened to his family in Vukovar. Abby goes too far when trying to arrange for a bone marrow transplant. Weaver back from suspension charms the young son of a hospital nurse.

Malucci treats a little girl who was molested by her father. David surprises Corday by giving her a necklace that once belonged to his late wife, with David's illness frustrating Corday as she treats a young woman who's actively trying to kill herself. Hathaway's birthday is anything but happy. Benton and Kovač clash over follow-up care. Carter seems reinvigorated but also ignores the orders of his supervisors. Greene makes amends with David shortly before he passes away.

Do open arms still await her in Seattle? Touched by a family tragedy at the ER---a dying DNR cancer patient whom she hopes to keep alive just long enough for her young children to say their goodbyes---Hathaway realizes she must see Ross. Chen notices Carter's increasing unreliability and mood swings. Hathaway admits to Kovač that Ross is the love of her life but she urges Kovač not to stop looking for love. Abby is supervised by Malucci on a case that leads Corday to tell him that no one at County thinks he is any good at his job. Greene urges Carter to therapy. Corday returns the necklace to Greene, who then gives it to his daughter Rachel while showing her her late grandfather's favorite Chicago lakeside spot. Hathaway flies to Seattle and reunites joyously with Ross.

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NOTE 1: Final regular appearance of Nurse Manager Carol Hathaway

NOTE 2: George Clooney makes an uncredited cameo as Dr. Doug Ross. The actor agreed to film the short scene on the condition that there be no publicity surrounding the event in respect to Julianna's final regular appearance.

Kovač and Benton rush to the scene of a school shooting, leading to a confrontation over who is the most critical patient: the shooter or one of his victims. Kovac chooses the victim and Benton's furious at him as the shooter bled to death on route to the hospital. Benton and Corday later perform an incredible surgical feat to save the shooting victim. Carter is discovered by Abby injecting narcotics into his wrist while cleaning up after a trauma. His addiction now public, becomes a concern not only to the staff, but also their patients. Greene and Weaver along with Benton, Chen and Anspaugh stage an intervention in an effort to convince Carter to enter rehab, which he balks at until a violent outburst leaves him crying in Benton's arms. Kovač is left enraged and nearly crosses a red line when he can't prove a young pregnant woman stabbed herself to get rid of an unwanted pregnancy.