Dr. Carter and Abby explore their budding romance under the confines of a quarantined hospital. The CDC looks into the mysterious outbreak as all hell breaks loose in the ER. Dr. Romano looses his arm in a freak helicopter accident and Dr. Lewis fights unsuccessfully to save an older man’s life in the stairwell.
Dr. Corday returns to the ER for the first time since Dr. Greene's death. Carter and Abby continue their romance. Gallant is challenged by a Psych shift.
A patient pulls a gun on Dr. Chen until his demand for Demoral is met. Dr. Carter, fed up with the hospital's poor security, stages a walkout and demands better security including metal detectors. Dr. Lewis empathisizes with an elderly woman whose son is dying of Huntington's disease. Dr. Kovac treats an HIV positive boy.
Carter and Abby argue over Abby's drinking problem. Luka flirts with a female patient's mother and gets caught in the closet with her. While demonstrating flu shots on live TV, Weaver accidentally sticks two reporters with the same needle.
It's Halloween in the ER, but Carter and Abby are the only ones in costume. The ER is packed with victims from an apartment fire. Dr. Corday treats a man with a flesh-eating infection. Luka treats a man with a constant erection. And a new surgical intern has a rough first day in part because he suffers from Parkinson's.
The new surgical resident gets into a heated disagreement with Dr. Corday about a patient. Dr. Chen feels threatened by a young patient. Elsewhere, Abby worries about her brother's strange behavior.
Dr. Carter and Chen handle a nanny with an unintended pregnancy; the staff objects to the behavior of a patient (Don Cheadle).
Abby tries to locate her missing, manic brother and asks their mother to help prevent his court-martial.
Abby and her mother disagree over how to handle Eric; Dr. Pratt has concerns for a young patient; a mother leaves her baby behind after birth.
Storyline unfolds in reverse order-style; Dr. Kovac collides with another vehicle on an icy road, and a bizarre cast of characters are treated at the hospital.
As Weaver tries to hide that she's pregnant, Chen helps some students who OD'd on uppers.
Dr. Weaver is put in a difficult position when a prominent and influential alderman tests positive for syphilis. Meanwhile, Dr. Carter is impressed by a hot-tempered doctor who, it turns out, runs an inner-city clinic.
Dr. Carter leans towards being a doctor in Africa.
Abby gets the call that her disturbed brother has gone missing. The ER must deal with the aftermath of a car hitting a group of teens. Dr. Weaver gets promoted.
Abby's mother compounds her frustrations. Weaver takes on a thief. Lewis finds a new fan.
Police accuse Pratt and Gallant for involvement in a crime at the diner near the hospital. Dr. Lewis spends time with a teenager confronting death.
Dr. Weaver gives the Alderman's lover favored treatment. Kovac tends to a girl who says that she was abused and Carter handles a malicious woman who has been poisoned.
Dr. Romano ruffles feathers as he takes over control of the ER. Kovac asks for Corday's assistance in securing treatment for a dying Croation child.
Abby waits for word on her missing brother. Carter receives news about his grandmother. Romano continues to cause havoc in his reign over the ER.
Carter tries to deal with a taxing day on the job after his grandmother's death and he tries to prevent further death at the hands of a revenge-minded gang member. A minor leaguer brought up to pitch for the Cubs suffers heart problems. Lewis tries unsuccessfully to distance herself from the man she married in Vegas. Kovac tries to help a Croatian boy get the proper medical attention.
The ER stays busy during a solar eclipse as Carter deals with the victims of a cult incident. Pratt works towards finding a baby torn from its mother's womb. Romano has to step around to the other side of the knife.
Carter and Kovac work to save people in the Congo but wonder who will save them when they find themselves caught in the middle of a war.