The air conditioning quits on the hottest day in October which, coupled with closed ERs in Chicago's other two hospitals, leads to an extremely hectic day. Dr. Ross treats a six-year-old suffering from a cocaine overdose; Ivan Gregor, the liquor store owner, shoots and seriously wounds a young teenager. Susan's immature sister Chloe drops by, wreaking havoc in Susan's life. Doug picks up a pharmaceutical saleswoman, much to Carol's displeasure.

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'.

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 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 worries about a Russian girl with AIDS who's brought in and then abandoned by her foster mother. Kayson asks Susan to be his Valentine. Deb accidentally consumes LSD-laced chocolates.

Dr. Hicks berates Benton when he tries to switch shifts to attend his mother's birthday party. A teenage girl, a frequent patient of the ER, is brought in for a drug overdose. Carol decides she wants to adopt Tatiana while Tag isn't so sure. Dr. Ross slugs an abusive father in the lobby. Jen accepts a job offer in Milwaukee despite Mark's offer from Morganstern. Deb and Carter await the arrival of sub-internship applications.

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.

A busy Dr. Greene goes all day in solving his patients' problems until he encounters the case of a pregnant woman suffering from complications that threaten both her life and her unborn baby's.

Mark, still upset over the loss of Jodi O'Brien, takes the night off but ends up in the ER anyway, albeit an hour late, when the new chief runs a drill at 2:00 a.m. Benton begins to realize his mother's future is not bright. Carter and Deb compete against each other. A small moon coinciding with the naturally heavy Saturday night traffic causes an exciting night.

Deb and Carter compete furiously for procedures after Benton announces their books are due a week earlier than previously announced. Deb commits a nearly deadly error on a patient while trying to keep up with Carter. Doug's relationship with Diane Leeds grows. Peter and Jackie decide to put their mother in a home. Dr. Greene is put on trial, so to speak, in the M conference for Jodi O'Brien. Chloe returns.

Susan is forced into the role of parent when Chloe gives birth and both Chloe and her mother, Cookie, shirk responsibility. Doug is surprised and a bit frightened when Diane suggests they move in together. Unfortunately, Linda Farrell happens to be around to take advantage of his nervousness. Carter is offered the ER sub-I but turns it down in anticipation of receiving a surgical position. Peter receives unpleasant news; his mother has died.