Dr. Carter struggles to overcome his chemical dependency in a detox center while Dr. Greene returns from vacation to find the ER awash in garbage during a custodial strike -- and a riot during a high school football game further clogs the halls with the rival wounded. Meanwhile, Greene finds unexpected complications when he treats the first victim, a likable injured player, and discovers that he must also minister to himself for a rash caused by poison ivy. Abby arrives back from another rotation and tries to help an elderly man whose wife is dead on arrival; later, she's furious when her ex-husband jeopardizes her clerkship when he does not pay her tuition. Dr. Benton grits his teeth when he interviews for an attending -- a lucrative supervisorial position -- with Dr. Romano.

A sympathetic Abby takes pity on a young couple whose premature baby was born far too early -- a cold fact of life which the desperate parents struggle to accept -- while Drs. Greene and Corday re-define their relationship in the wake of domestic hassles. Dr. Benton engages an equally stubborn Dr. Romano in a war of wills over an obnoxious homeless man who once again requires extensive treatment resulting from his chronic disdain for maintaining his dialysis appointments. Dr. Weaver and a caring Dr. Kovac are helpless to assist a severely comatose woman whose longtime life partner is not legally empowered to cease any heroic means of saving her. Elsewhere, Carter ponders the implications of his future return to the hospital and Dr. Malucci stays out of sight from a candy striper who's on a mission to find him.

Dr. Benton learns the sobering price of a previous challenge to the authority of tyrannical chief Dr. Romano while a recovering Dr. Carter chafes under the restrictions imposed on his role during his first day back in the emergency room after his drug treatment. Likewise, obstetrics nurse Abby is peeved when she is beset by nagging hassles and is asked by Dr. Weaver to fill in as an ER nurse until she can re-enroll in medical school. The collapse of an elevated walkway in a sci-fi convention floods the ER with out-of-this world costumed patients while Dr. Corday must talk Dr. Greene through a complicated procedure via an intercom while she too performs surgery. Ambitious desk clerk Frank -- a former cop -- causes chaos when he keeps running computer security checks on suspicious patients with surprising results. Another patient checks in claiming to suffer from spontaneous combustion.

A frustrated Dr. Benton desperately searches for a new position at any local hospital but soon learns that he has been blackballed by the arrogant Dr. Romano, and he must consider other options out-of-state -- even though he risks losing joint custody of his infant son with the combative mother. Elsewhere, a recovering Dr. Carter is cleared to work on a few trauma patients while Dr. Chen labors to offer a young mother some temporary relief as she tries to secure permission to operate on the woman's terminally ill young son. Abby finds herself attracted to Dr. Kovac but their budding relationship is interrupted by tragedy. In addition, Dr. Malucci casts about in a vain search for an extra skilled hockey player for his team's game that night -- even though Dr. Greene is ready and willing to strap on his skates.

Dr. Greene risks his life when he accompanies a dangerously weak heart patient in an emergency helicopter that crashes en route to the hospital. While Greene tries to encourage the sick man not to give up hope of a transplant that will enable him to marry his fiancee, Dr. Benton is ordered by Dr. Romano to manage a flood of angry, hurting people as he substitutes for Dr. Weaver on a short-staffed day in the E.R. Elsewhere: Abby is fearful for a distraught Dr. Kovac when he does not show up for work after a personal trauma; and Dr. Carter gambles when he ignores a relative's wishes not to inform her teenaged grandson that he carries the HIV virus.

An anguished Abby flinches when she is unexpectedly visited by her unpredictable mother while Dr. Benton is shocked to discover details about a severely wounded gunshot victim. Meanwhile, Drs. Greene and Corday pledge to each other that they will escape the ER for a weekend getaway but complications ensue when she must perform surgery on a middle-aged surfer with a bad back. Dr. Kovac suspects that a young teenaged patient -- who proves to be pregnant -- might have been assaulted by her father. Dr. Chen finally confronts the unsuspecting father of her baby.

A stormy Thanksgiving workday in the ER results in a cornucopia of milestone events as a thunderstruck Dr. Greene receives disturbing news while a woozy Dr. Corday is sued for malpractice -- and Abby tries to send her unstable mother off, but the broken woman has no place else to go. Dr. Chen is caught by surprise by her high-tone mother who does not know about her pregnancy. Elsewhere: Dr. Benton's pay is docked by Dr. Romano; Dr. Carter chases down an impatient patient who needs immediate treatment; and an explosion rocks the ER.

Abby's mounting frustration with her bipolar mother goes off the charts when the woman causes a major incident at a downtown store. An uneasy Dr. Corday confronts her accusers during a tense, day-long deposition when she and the hospital are sued by a paralyzed former patient. A mourning Dr. Benton meets his nephew's beaten girlfriend who informs him about the gangbangers responsible for the murder. Greene is concerned that Dr. Carter isn't maintaining the conditions of his drug treatment program. Abby's relationship with Dr. Kovac heats up but she seeks consolation from her family woes with Carter.

Christmas is just days away, and Dr. Greene accompanies Dr. Corday to New York on a mission during the holiday season. Dr. Carter fights fatigue as he assists Dr. Chen during the birth of her baby. However, Carter notices that Chen's attitude toward her unwanted baby may be changing even as the adoptive parents wait patiently for their new child. In addition, Carter must fight against temptation to ruin the progress of his drug rehabilitation program. Elsewhere: Dr. Benton receives an ultimatum from Dr. Finch to remove a wayward teenaged girl from her residence; Dr. Weaver treats a boy whose face is badly mauled by a dog.

New Year's Eve falls as Dr. Greene submits to dangerous, experimental brain surgery in New York with a hopeful Dr. Corday by his side while a guilt-ridden father who is severely injured in a car wreck is only concerned with the safety of his teenaged son who is also hurt. However, the dad's condition deteriorates as the irascible Dr. Romano is called on to begin desperate heart surgery and Greene's radical procedure soon develops complications.

Dr. Benton's relationship with Cleo is further strained when the wayward teenaged girl whom he's trying to help resists his efforts to move her out of Cleo's residence and into a foster home while a bishop who's injured in a fall takes an interest in the brooding Dr. Kovac. Elsewhere: Kovac resents having to treat a drunken driver who's responsible for tearing apart a young family; as Dr. Greene recovers from his surgery, Dr. Corday recents some jolting news about her malpractice suit; Dr. Carter is urged by Abby to confront Dr. Weaver about his recent temptation to take narcotics; Weaver clashes with Dr. Legaspi over personal as well as professional issues.

Dr. Weaver regrets her decision to report a work-related injury in an illegal sweatshop when the corrupt owners panic and try to eliminate the evidence by torching the premises -- with the illegal alien workers trapped inside -- while Dr. Greene returns to work with a curious change in his attitude and personality. Elsewhere, Dr. Benton is sandbagged by the wily Dr. Romano who lures him into a new position without confiding the political implications of the new job. After confessing his temptation to Weaver, Dr. Carter is restricted from issuing controlled narcotics. Abby treats two combative elderly men who are injured while fighting each other. Dr. Corday wavers again during surgery and risks her career.

Dr. Carter must attend a charity event hosted by his grandfather and cajoles Abby into filling in as his date at the last minute while Dr. Kovac treats an ailing Bishop Stewart and a 16-year-old in need of a third heart transplant who both insist on treatment that could threaten their lives. Also, Dr. Malucci is surprised by a patient's reaction to some HIV test results, and most of the staff -- especially Dr. Romano -- takes notice of Dr. Greene's new and aggressive post-surgery attitude.

Dr. Greene is angered when his post-operative competency is challenged by a medical review board that could cost him his career while a tormented Dr. Kovac can no longer ignore his crisis of faith when he accompanies an ailing but stubborn bishop to a priest's ordination. Elsewhere: Dr. Carter struggles to save the life of a child whose parents refused to immunize him against measles; Dr. Benton chafes in his new added role as director of diversity when he encounters a low-rated African-American applicant who reminds him of himself as a young student; Dr. Weaver recoils when she meets Dr. Legaspi's fellow lesbian friends; Dr. Chen returns after her maternity leave.

In the classic drama’s 150th episode, a multi-car train accident scrambles the ER and Drs. Kovac, Carter and Corday are overwhelmed by the carnage at the site as they work to save an impaled mother, her young son and a trapped firefighter -- until the pregnant Corday begins to suffer painful contractions. Back at County, Dr. Benton tries to salvage a victim with a shredded aorta and even helps Carter with a tricky amputation over the phone, all of which leaves an observing med school applicant wide-eyed. Meanwhile, the bloody mayhem prompts Kovac to recall the harrowing loss of his own family and he confronts his torment with the terminally ill Bishop Stewart.

Dr. Weaver's difficult life is further complicated when she fears her intimate relationship with Dr. Legaspi might be exposed when the suicidal young woman who earlier caused a deadly train derailment claims Legaspi sexually harassed her, while elsewhere, a guilt-stricken Abby launches a desperate search for a stolen baby under her care. In addition: Dr. Carter is dumbfounded when he learns more about his young new romantic partner; Dr. Greene awaits word on his medical competency tests; a pregnant Dr. Corday struggles back to work and runs headlong into the obnoxious Dr, Romano, who is on the warpath and intends to marginalize her responsibilities; Dr. Malucci also butts heads with a belligerent father; and a newly re-awakened Dr. Kovac re-evaluates his life and relationship with Abby.

Dr. Benton is a horrified bystander as the elderly black patient he is treating grabs a cop's gun with tragic results. Dr. Carter, who is rethinking his relationship with Rena, teams up with Abby to treat a class of seventh graders who become sick on their bus from mysterious toxic fumes. Meanwhile Dr. Greene learns the results of his review; and Dr. Corday is determined to prove to Dr. Romano that she can still pull long hours in the O.R.

On their rainy wedding day, Drs. Greene and Corday must fight fate to get to the altar as he overcomes several roadblocks until he is waylaid in the street by a nasty bleeding pregnant woman -- meanwhile, she contends with last-minute details and her feuding divorced parents. Elsewhere, several ER staff try to free themselves from work to attend the ceremonies, including Dr. Finch and Dr. Benton, ever mindful of the irony that he once dated Corday. However, the uninvited Dr. Weaver heads for an out-of-town medical conference and meets a friendly and appreciative man. When a prison van overturns, Dr. Carter tries to save the life of a crushed corrections officer -- and gets some ribbing about his young girlfriend -- while Abby treats a teenaged female prisoner. Dr. Chen ministers to a hypothermic boy found asleep on a frozen field.

A tense Abby drops everything when notified that her mentally unbalanced mother is found incapacitated in an Oklahoma motel, and when she insists on driving there, a sympathetic Dr. Carter accompanies her -- risking both of their romantic relationships. In the meantime, the road back is potholed with problems as they try to coax the disconnected woman back to Chicago for more professional help. Elsewhere, the very pregnant Dr. Corday is happily wheeled in for her baby's birth with Dr. Greene at her side. An angry Dr. Benton treats a parade of partying fraternity brothers whose alcohol-related medical problems become increasingly more serious; later, Benton offers special care for his former junior high school teacher who jump-started his interest in science as a youth.

Due to a clerical error, a startled Abby discovers that her suicidal mother is due in court for a competency hearing and she rushes to testify that she should not be released -- but the older woman musters an alarmingly masterful display of sanity before the judge. Meanwhile, Dr. Weaver gives heartbreaking news to a sassy homeless woman who once hosted a children's show that Weaver viewed as a child. Dr. Benton steps in to help a junior high school teacher who was once his mentor and now suffers a cardiac arrest. A busy Benton also injures his hand while helping a fallen biker and learns that an injured Carla has checked into the ER with his young son Reese. A perplexed Dr. Carter treats a stricken pregnant woman and then is angered when her husband informs him about what prompted her life-threatening episode.

A distressed Abby sees a ray of hope in the care of her mentally unbalanced mother when she receives some sage advice from the older woman in a rare moment of clarity while Dr. Benton's old girlfriend Carla squares off against his new love Cleo. Elsewhere: Dr. Greene's suspicions are aroused when he treats a rebellious 7-year-old boy who bears signs of beatings; Dr. Carter's plans to apply for chief resident are brushed aside by Dr. Weaver while he watches fellow candidate Dr. Chen take her best shot at the position; Weaver suffers pangs of remorse when she meets the new woman in Dr. Legaspi's life and is confronted by a helpless, mentally deficient young woman whose only family member lies in critical condition; and the ER gang enjoys a spirited game of softball.

The ER is overwhelmed with gunshot victims when a distraught father goes on a murderous spree at a foster care facility -- and a horrified Dr. Greene realizes that his personal connection with the madman may prove fatal for his new wife and their baby. In the midst of the chaos: Dr. Carter is put in the awkward position of helping Dr. Chen apply for the promotion that he himself was denied, Dr. Benton is unexpectedly assaulted by his ex-girlfriend Carla's husband, and Dr. Finch cuts her hand while treating an HIV-positive patient. Meanwhile, Dr. Romano betrays his prejudice when he tries to force out Dr. Legaspi.