John Carter, a third-year medical student, begins the first day of his rotation in the ER at County General Hospital. Dr. Mark Greene, an ER resident physician, considers an offer to go into private practice. Dr. Susan Lewis, another ER resident, deals with myriad patients, including one diagnosed with advanced cancer. Dr. Doug Ross, the ER pediatrician, confronts a woman about potential child abuse. The head nurse, Carol Hathaway, returns several hours after her shift as a patient, following an apparent suicide attempt.

Lewis butts heads with the resident psychiatrist, Dr. Div Cvetic, over care for a senile patient. Greene deals with an elderly man who insists on keeping his wife on life support despite her DNR request. Benton corrects a diagnosis made by his own physician. Carter is seduced by a patient. A family comes in after an alcohol-related car accident. Greene's wife has passed the bar exam, but their celebrations are interrupted. Ross visits Hathaway, who is recovering from her suicide attempt.

Hathaway returns to work after her suicide attempt, and gets support from her co-workers and her orthopedic surgeon boyfriend, Dr. John "Tag" Tagliari. A mysterious woman comes to the ER and sings to the doctors and patients while the doctors try to find out who she is. Lewis deals with a heart patient. Benton works with an injured convenience store clerk who insists on defending himself when his store is robbed.

Ross attempts to reconcile his lingering feelings for Hathaway while dealing with a single mother and her young son after it is found that she hears voices. Benton clashes with another surgeon over a hit-and-run patient. Carter must make the notification to the parents of a young boy. A married man comes in suffering a mild heart attack while handcuffed to his mistress.

Greene mulls a decision to move to Milwaukee so his wife, Jennifer, can pursue her law career. He and the rest of the ER staff tend to a dying heart transplant candidate. Ross counsels a woman who cannot afford medication for her asthmatic daughter. Carter may have made a mistake with a former patient. Lewis has to juggle dealing with an alcohol-poisoned fraternity brother and calls from her mother to get her prodigal sister, Chloe, a job.

The air conditioning at County General is broken. Greene brings his daughter, Rachel, to work with him while Jennifer goes apartment hunting in Milwaukee. Ross works with a 5-year-old girl that ingested cocaine. Benton tries to save a young robber shot by his frequent convenience store clerk patient. Lewis tries to deal with Chloe's worsening mental problems.

Ross and Hathaway save a young boating accident victim. They give in to their feelings briefly, making Hathaway reconsider moving in with Tag. Chloe disrupts a date between Lewis and Cvetic. Benton is competing for a prestigious fellowship. Greene observes Carter in the ER, giving Carter some confidence.

Greene calls in sick so he and Jennifer can spend the day together, leaving Ross in charge of the ER. Carter works on a high school wrestler that starved himself to make weight. Hathaway counsels a young rape victim. Benton is dealing with his senile mother, and butts heads with Ross. Lewis is worried about Cvetic's growing temper problem.

Lewis is caught in the middle as both Cvetic and Chloe have problems. Carter tries to help a suicidal transgender woman. The ER tries to save two boys who killed a girl in a car accident. Benton invites Carter to Thanksgiving with his family. Hathaway confesses her feelings about Ross to Tag after Ross begins a new affair.

It's a December blizzard, and the day starts out quiet. Hathaway announces her engagement with Tag. Suddenly, County General goes into crisis mode when a 32-car pileup on an expressway inundates them with patients. Among the patients are a young male that Benton knows that lost his leg, a patient of Ross' that dies suddenly while waiting for treatment, and a man who is snowed in at home and calls Greene when his wife refuses to go to the hospital to have her baby. Lewis tries to save a man that suddenly develops an aneurysm, and the patient is saved by the most unlikely person.

A transfer team is due by helicopter to receive donor organs - but Benton has not yet obtained next-of-kin approval for the organ harvest. And although it's Christmas Eve, Greene has not found time to shop for gifts. Ross crashes a party.

Carter proves he's ready for the OR - but his first day in surgical attendance is a comedy of mishaps. The consequences are grave when Lewis discharges a cardiac patient. Benton must deal with a family conflict.

The nonstop parade of crises and stricken young innocents weighs heavily on Ross. Meanwhile, the heart attack victim under Lewis' care is the doctor who nearly wrecked her career. Benton hires a physical therapist, Jeanie Boulet, to take care of his mother.

Morgenstern surprises Greene with a new job offer. A terminally ill breast cancer patient asks Greene to help her die. An armed boy threatens the hospital staff.

Kayson pursues Lewis romantically. Ross and Hathaway cope with a young Russian girl with AIDS whose adoptive mother abandons her. A humane policeman hauls in a dog he hit with his car.

Greene and Benton each have family birthday parties to attend, but ER demands may keep them away. Meanwhile, Carter mistakenly thinks it's Benton's birthday and hires belly dancers as a celebratory surprise. Hathaway considers adoption.

Benton runs on no sleep for 48 hours. A con man works the floor. A mental patient poses as a hospital efficiency expert. Greene's wife wants a divorce. Hathaway's past comes back to haunt her.

Greene misdiagnoses a pregnant patient, leading to a long and arduous surgery.

The moon is full and so is the ER - filled with popsicle pledges, a would-be werewolf, and others affected by "lunar lunacy" - and Lewis is the only resident available. Coping with emotional problems, Greene's not making a good impression on the new ER chief.

Greene must lead seminar on the ill-fated pre-eclampsia case he recently misdiagnosed. The rivalry between Carter and Chen causes Chen to make a disastrous mistake. Lewis' pregnant sister Chloe returns from Texas.

Benton compensates his inability in helping his mother by going beyond the call to help his patients. Meanwhile, Greene attempts to save his marriage - but that means less time at work and more disfavor with the new ER chief.

Carter's family background is discovered. Benton starts falling for a married woman. Hathaway has trouble writing her wedding vows. Greene is living with his wife in Milwaukee, but their marriage is still broken. Lewis treats a suicidal patient.

Ross must deal with commitment issues. Carter's future is uncertain. Lewis helps deliver her niece. Benton receives some bad news about his mother.

Both Greene and Carter get some surprising news. At Hathaway's wedding, not everything goes as planned.