The fifteenth and final season of the American fictional drama television series ER premiered on September 25, 2008, and concluded on April 2, 2009, in a two-hour episode preceded by a one-hour retrospective special. It consists of 22 episodes. Because actors Mekhi Phifer, Goran Visnjic, and Maura Tierney had been told the 14th season would be the last one, they had no plans or interest in returning for S15. The producers agreed to film two S15 episodes at the very end of the Season 14 production cycle so that all three actors could finish their time on the show and move on to other projects. Tierney would make a one-scene guest appearance in an episode near the end of Season 15.
Plot
The final season opens up revealing Gregory Pratt is the victim of the ambulance explosion. Despite the rallying efforts of his workplace colleagues, he succumbs to his injuries and dies. The season introduces Cate Banfield as new ER chief, a woman with a seemingly mysterious past with County General. Luka Kovač and Abby Lockhart leave for a new life in Boston, Brenner must deal with issues surrounding his childhood, and he comes to a crossroads in his relationship with Neela, Samantha Taggart and Tony Gates' relationship suffers a major setback after an accident involving Alex Taggart while Neela Rasgotra is forced to make some tough decisions, both personal and professional.
To mark the end of the series after 15 years, several former cast members make a return to the show. Mark Greene, Robert Romano, and Kerry Weaver appear in a flashback episode that explores Banfield's history with County General while John Carter returns to work at County although, unbeknown to his colleagues, he is in desperate need of a kidney transplant. Peter Benton, Doug Ross, Carol Hathaway, Susan Lewis, Elizabeth Corday, and Ray Barnett return in various episodes. The series ends with one final multiple casualty incident that brings multiple patients to the ER, and shows that life goes on at County General.
Mimi Leder, a frequent director during ER's first two seasons, returned as a director for the episode "A Long, Strange Trip"
Rod Holcomb, the director of the 1994 pilot episode as well as several other early episodes, returned to direct two episodes in this season, among them the series finale
Paul McCrane, recurring cast member seasons 4 and 5, and series regular seasons 6–10, continues his affiliation with the show as director of two episodes this season
Gates hurries to the scene of the ambulance explosion after learning it was Pratt, not Sam, in the ambulance. Pratt is rushed back to County suffering from blast injuries, where the ER staff work to stabilize him. Eventually, a carotid tear develops, and despite the rallying efforts of his colleagues, he dies. Meanwhile, Abby misdiagnoses a patient, and talks about her plans to leave Chicago to start a new life with Kovač, while Morris must pick up the pieces after Pratt's death.
A new batch of interns as well as the new head of the ER arrive for their first day at County. While adjusting, a bio-terrorist with a bag full of Ricin is admitted with a broken leg.
Abby gets a job in Boston and tries to leave County General quietly, but the staff makes it known how much they will miss her. Abby says goodbye and leaves for Boston with Kovač and her son.
NOTE 1: Final appearance of Dr. Luka Kovač and the final regular appearance of Dr. Abby Lockhart.
Dissatisfied with the interns' performance, Banfield decides to start a new system. Each intern gets a mentor with daily two-way crits: Daria is paired with Gates, Ryan with Morris, and Tracy with Brenner. Brenner tells Tracy how he wants to proceed, but she insists on doing things her way. A girl comes in with a broken leg which may be caused by a severely mentally ill family member.
Sam's time is taken up by her studies for a pharmacology exam, leaving Gates feeling neglected. A school fight results in a stabbing, with Brenner treating the victim and trying to uncover the truth behind the story. Morris has a surprise for Neela. Gates gets locked in a stairwell with a quiet young boy on Halloween night.
Banfield is upset when her husband Russell (Courtney B. Vance) insists on a visit with his parents; Morris treats a young boxer (Chadwick Boseman) whose father (Carl Weathers) wishes him to quit, during treatment Morris favors Chaz over senior interns, resulting in trouble; Gates asks Sam and Alex to move in with him and treats a war veteran.
Banfield must deal with the ghosts of her past when a critically ill child arrives in the ER. A past encounter with Mark Greene helps her diagnose and confront her own problems. Neela's intern loses his first patient, and struggles to cope.
NOTE: Final appearance of Dr. Mark Greene and Dr. Robert Romano.
A man acquitted of child molestation comes into the ER with his wife, who was injured when their house was set on fire, drawing Brenner's hostility. Later, the man's interest in a young girl leads his brother-in-law to beat him, nearly blinding him. When Brenner becomes emotional while the man is treated, Morris confronts him, leading to an emotional revelation about Brenner's past. Neela's frustration with her intern reaches the boiling point, and Dubenko teaches her a lesson in the importance of teaching and mentorship. Gates continues his search for the missing veteran.
While snow strands Banfield and Morris at a doctors' conference in Omaha, Gates is left in charge of the kids. He allows Sam's son Alex and Sarah to walk through the blizzard to a nearby party. Driving a friend's car after the party, Alex is gravely injured as he crashes in the storm. Sam goes ballistic.
Morris receives an unwanted package from his father at the ER doorstep. Sam is anxious about getting Alex off of the ventilator after his accident. Meanwhile, a pregnant woman with a high-risk pregnancy is in danger of getting deported and a batch of brownies have some interesting effects to staff that eat them. Sam tells Gates that she and Alex are moving out.
The ER treats two brothers who are shot during a drug deal. Banfield and her husband continue their quest to restart their family. Sam and Gates argue while treating patients.
Neela has a series of three dreams where the outcome of the lives of two patients depend on her decisions. In the first two dreams, she makes either of two choices, but each one kills the patients. In the third dream, she makes a new choice, saving the lives of two patients as well as sleeping with Brenner. In the end, it is revealed they were all dreams. Meanwhile, Banfield and Morris are still at odds and Banfield goes home.
Morris treats a youngster who was hit while riding her bike. Meanwhile, Gates has trouble distancing himself from Sam; and Neela's nerves take over when she learns Brenner has returned from Australia.
Dr. Morgenstern visits County General upon learning a former mentor is seriously ill. Meanwhile, Sam's sister (Shannon Woodward) drops by unexpectedly; Gates and Morris treat an elderly man (Rance Howard) who was assaulted on the street; and Brenner is shocked by a patient's diagnosis.
A mother is severely injured by a car accident in the ambulance bay; an insurance company frustrates Morris and he gets a major surprise; Neela tells Brenner about her offer in North Carolina. Meanwhile, a man refuses treatment and Gates and Neela try to get him to consider treatment.
Valentine's Day in the ER sees Neela and Brenner growing closer. Banfield tries to convince her husband to go along with her new plan to have a baby. Gates treats a patient who may have ingested a toxin while "mushroom hunting" while Neela performs surgery on a young girl's mother. Morris and his girlfriend clash when he suspects her fellow officers physically assaulted a badly injured patient. Carter returns to the ER for a visit, gets the OK from Banfield to do some shift work at County, and is seen on hemodialysis in the final scene.
The Banfields explore their options with an adoption agency. Carter struggles with the new procedural and technological advances made to emergency medicine since he has been gone. Brenner confronts Lucy's foster family about his concerns. Morris treats a couple who takes his advice too far. Sam is shocked when her mother is brought into the ER. Neela makes a decision about her future at County. Banfield discovers Carter's medical condition.
A camera crew shooting footage for a documentary descends upon the ER. Detective Claudia Diaz is brought in with life-threatening gunshot wounds. Neela is perplexed by the lack of communication between her and Brenner. Sam struggles to reconcile with her mother. Carter's condition suddenly worsens.
As Carter awaits his kidney transplant, he gets a surprise visit from Benton. Meanwhile, Ross and Hathaway must receive consent for organ donation from a woman who is grief-stricken over the sudden death of her grandson, but Sam and Neela are stuck at the airport with the transplant organs in hand. Banfield bonds with an abandoned baby. Brenner continues to care for a little girl whose mother is awaiting a heart transplant.
NOTE: Final appearance of Dr. Doug Ross and Nurse Carol Hathaway.
Neela clashes with Dubenko on two surgical cases and looks to prove her worth as attending material before she leaves County for good. Brenner looks to gain some insight into his abusive childhood.
NOTE: Final appearance of Dr. Lucien Dubenko and Dr. Abby Lockhart.
A woman returns to County to claim the baby she had abandoned there. The ER doctors and nurses assist at a camp for children recovering from open heart surgeries where Morris proposes to Claudia and Brenner befriends a kid who does not want to join in with the activities.
Series finale. A new medical facility for the underprivileged funded by Carter is opened and old colleagues return to show their support. Gates treats a teenager with alcohol poisoning after she and her friends play a drinking game. Sam is surprised when she receives a special gift for her birthday. This two-hour episode was preceded by a one-hour retrospective special. At the end, a multiple casualty incident brings multiple victims to the ER and County General is seen for the final time.
