Mark learns that his tumor is back and inoperable, giving him 4-5 months to live. Corday is living in a hotel, and confesses to Benton that she thinks she's left Mark. Susan cares for Mark after his first radiation treatment. Abby learns that the case against Brian has been dropped because somebody beat him up. Seeing Brian enter her building, she seeks comfort at Luka's, where he's engaged in a game of Pictionary with his friends. Jerry and Frank clash, leading to a fistfight. Chen has a stalker.

The episode was rated 7.56 from 94 votes.

Eleanor Carter tends to a young leukemia patient, trying to make up for Bobby's death many years ago. Mark treats the victims of a letter bomb, and later treats his own daughter when Ella is rushed in after swallowing some of Rachel's Ecstasy. Abby treats a young girl who has been chauffering her drunken mother around. Abby also hides Joyce in her apartment while Brian searches for her and causes a ruckus. An allergic Gallant treats a blind man with a dog. Chen returns to the day shift, working with Weaver for the first time. Romano gives some of Weaver's duties to Lewis, making Kerry mad, until she meets a new friend on her way home.

The episode was rated 7.57 from 102 votes.

Susan and Carter treat a newlywed couple where the wife may be allergic to her husband's semen. Carter later kisses Susan. Weaver asks firefighter Sandy Lopez out. Mark and Gallant treat members of a boxing family. Rachel's boyfriend is admitted with a broken ankle and tests positive for marijuana; she comes out clean though. Elizabeth tends to a comatose woman whose husband will only agree to a risky procedure to harvest her organs. Abby openly questions Nicole's pregnancy; Nicole confesses to Luka that she was faking it and that she plans to move to Montreal. Benton's custody trial for Reese is hampered by his long hours. Cleo's testimony doesn't go well either.

The episode was rated 7.58 from 100 votes.

A new med student assigned to Carter finds all sorts of surprises in store for him on his first day. Elizabeth spends her day searching for the angel of death, finding that all signs point towards Dr. Babcock. Nicole has a rough day training to become a nurse's aide, and draws Abby's ire after Luka invites her into a trauma. Puzzled by his grandmother's fainting spells, Carter discovers that she is at great risk for a heart attack or stroke. He and Susan treat a law student/med student who has been cutting herself. The two grow closer, as Carter finally tells her about his stabbing and drug addiction. Mark picks up Rachel at school after she's suspended. Peter is sued by Roger for custody and takes a DNA test to determine whether he is Reese's real father. Despondent over badly injuring a young skateboarder, a mall security guard tries to hang himself.

The episode was rated 7.59 from 96 votes.

Corday, still living in the hotel, is avoiding Mark, until Ella says her first words. Elizabeth pressures Susan to tell her what her husband is hiding, and figures out her husband's fate. Romano advises her to return to Mark for the little time he has left. Chen treats a man too traumatized to speak. Mark tells the staff about his prognosis. Weaver worries about Sandy Lopez as she is reported missing in a fire. Weaver tracks her down at a bar, and the two make out. Stabbings on a college campus bring girls to the ER.

The episode was rated 7.63 from 102 votes.

Abby wakes up at Luka's while Carter finds Susan returning from spending the night at Mark's. A dominatrix's client is brought into the ER, and she leaves a bag of her toys behind. Abby, Carter, Luka, Susan and Gallant explore in the bag, until Weaver catches them. Susan tries to take responsibility, until Weaver finds a purple dildo in her locker and sends them all to an all-day sexual harassment seminar. While waiting for the tardy instructor, everybody learns a little more about each other. Luka and Carter actually have a duel. Susan and Abby bond, while Susan has doubts about her relationship with Carter. At the end of the day, they break up and Susan tells Carter to tell Abby that he's madly in love with her.

The episode was rated 7.63 from 101 votes.

Carter inquires about an attending position; Weaver pretty much turns him down. He also gets stuck at the hospital with a never-ending rush of patients from a stampede at a rock concert, and slips, hurting his back, while looking for Weaver. A frazzled Chen disappears for awhile, while Weaver goes to Doc Magoo's with her old private investigator--he's found her mother for real this time. Luka and Abby go to a bar; she gets mad when he ignores her and flirts with a French waitress, and they break up. Corday and Greene find it difficult to balance their schedules; she wants to hire a nanny to take care of Ella. Benton discovers that Carla died in a car accident; Reese was slightly injured also. Malucci makes a fatal assumption with a patient, which Chen signs off on anyway, earning them both Weaver's ire. They blame it on Weaver not answering their pages; we later see that Weaver left her pager in the bathroom at Doc Magoo's.

The episode was rated 7.65 from 91 votes.

Abby has a horrible birthday, beginning with meeting her new squabbling neighbors. She treats a young woman hoping to get pregnant by taking fertility drugs, and discovers that Luka is going to Bosnia for two months as part of the Doctors Without Borders program. Her ex-husband tells her that he's getting remarried just before she sees Carter and Susan sharing a private moment. She takes care of a young boy abandoned in the ER after the death of his mother. Paul Sobricki is admitted with a head lac, and Abby unsuccessfully tries to keep Carter from seeing him. Abby's day ends with her sharing a beer with her neighbor. Carter has problems of his own: his mother is back in town, just getting in the way and refusing to admit to her mistakes. He also meets with Chen, who reveals that she has the evidence to take Weaver down in the Marfan's case. Weaver and Lopez are an item until Sandy discovers that Weaver has not widely come out yet. Mark finds cigarettes and condoms in Rachel's

The episode was rated 7.65 from 100 votes.

Benton commits perjury on the witness stand in order to gain custody of Reese. When Romano refuses to give him a more even schedule, Peter resigns and seeks a job at the clinic where Cleo is newly employed. Benton is granted custody of Reese and he and Cleo decide to move to the suburbs together. Meanwhile, Carter's father visits for Christmas with the news that he's getting divorced, Weaver and Sandy Lopez finally go on a date, and Abby catches Nicole in the maternity ward, recovering from an abortion.

The episode was rated 7.67 from 94 votes.

Mark worries that his brain tumor may have returned, as Elizabeth tells him that she will leave him if Rachel is not sent back to St. Louis. Lewis has a busy day running the ER after several staffers come down with food poisoning after eating tainted bagels donated by a pharmaceutical company. Luka returns to cover shifts. Eleanor Carter flees the hospital after realizing how poor Mickey's condition is. Carter talks her into staying to comfort the boy during his treatment. Finding that Brian has beat Joyce yet again, Abby encourages her troubled neighbor to seek help in a group home. Brian later confronts Abby at her apartment and punches her for interfering. At County, Luka and Susan treat Abby, who has a broken nose and a few cuts and bruises. Luka finds Brian at a bar, and beats him, threatening to kill him if he touches Abby again.

The episode was rated 7.67 from 101 votes.

An enormous rainstorm pelts Chicago. Cleo's last day at County is interrupted by the arrival of Benton's DNA results: he's not Reese's biological father. Benton meets with his lawyer regarding the trial; she advises him to let Roger see Reese; he refuses. Money from the nurses' secret stash and Frank's Palm Pilot go missing, only to turn up in Nicole's purse. She later tells Luka that she's pregnant. Susan accuses Mark of being grumpy with his patients; he spends the day treating a kid who fell in the river with his younger brother and whose parents blame him. Weaver travels to an accident site, where Pickman's ambulance was rammed by an SUV. She treats a pregnant stab wound, going as far as to give her a C-section in the broken ambulance, with Gallant's help. Carter's grandmother comes in after being involved in a hit-and-run and breaking her hip. She becomes delusional in an MRI machine, calling out for her husband.

The episode was rated 7.70 from 93 votes.

The day begins slowly as Weaver calls to say she'll be late, and Chen thinks she's developing a fever. Then multiple MVAs come in, quickly followed by two children suffering what appears to be smallpox. The staff panics, but not as bad as the patients, when a lockdown is ordered for the ER. The feverish Chen is quarantined with homeless Stan. Lewis takes charge as Weaver arrives and the police won't let her in. The girl infected by smallpox dies and Pratt embarasses Carter in front of her parents. Carter notices Pratt is sick as well, and sends him to Chen's room. Jerry phones the news, and the patients riot, nearly using a gurney to break open the emergency bay doors. Control of the ER is relieved from Weaver by an infection specialist. The staff prepares to stay, still not having a confirmation on whether it is smallpox or not, and the lockdown continuing as a result. Carter and Abby kiss after being quarantined together.

The episode was rated 7.75 from 108 votes.

Carter is having back problems that aren't helped when Abby asks him to help move a new fish tank into Luka's apartment to replace the one she accidentally broke while moving out. Benton encounters problems finding a sitter for Reese when Jackie decides that she can't do it. Chen is having trouble with Weaver "helping" her with patients; she treats an abandoned infant with a birthmark in the shape of the sign of the Virgin Mary. Cleo's HIV test results come back negative. Rachel Greene shows up at the hospital; she ran away from Jenn and wants to stay with Mark for a while. Corday falls asleep in surgery. Malucci is stuck in an elevator with a cute female paramedic and a guy vomiting blood. After saving the guy's life, Dr. Dave is caught "celebrating" with the paramedic in the back of an ambulance by Weaver, who promptly fires him. Appealing unsuccessfully to Mark, Dave and Weaver finally have it out at the end of the day. He begs her not to fire him because he needs the money

The episode was rated 7.78 from 93 votes.

Mark serves his final day in the ER overseeing the first day of Gregory Pratt, a cocky yet eager new intern. Through observing his patients, he decides to forego chemotherapy, and spend his remaining days in peace. He also meets with his ex-wife, tells Weaver to live a little and leaves. Meanwhile, Abby plans to move back into her apartment when her landlord lets her know that Brian's moved out.

The episode was rated 7.88 from 103 votes.

Mark decides to use his remaining time to help "fix" Rachel and takes her to Hawaii to show her where he grew up. He teaches her how to surf, and how to drive a stick shift. Mark catches her chasing one of his Vicodin with a shot of vodka and confronts her about wasting her life. One day after surfing, he has a seizure, and Elizabeth arrives with Ella in tow. She wants to take him home, but he refuses. Early in the morning, he dies. After the funeral, Rachel tells Elizabeth she'd like to visit Ella, and Elizabeth agrees.

The episode was rated 8.21 from 119 votes.