The hospital remains in lockdown while the Centre for Disease Control and Prevention probes the lethal illness that requires the staff to be quarantined. Left alone, Lewis fights to save a patient.
Corday makes an emotional return and clashes with Weaver. Carter and Abby can't conceal their growing attraction to each other. Romano faces a daunting new challenge. Pratt infuriates his colleagues.
After an enraged drug addict points a gun at Chen and other staff members, an exasperated Carter leads a walkout. Abby's brother Eric witnesses more than he expected when he visits the hospital.
Gallant is upset by his colleagues' callous treatment of an elderly patient. Weaver makes a series of embarrassing mistakes. And Corday treats her husband's carer.
A suspicious fire on Halloween fills the ER with victims wearing fancy dress. Romano lets his recent history affect his decision making. Marquez threatens to file a grievance report against Kovac.
Corday clashes with new surgical resident Paul Nathan. Abby is concerned about the erratic behaviour of her visiting brother Eric, and frets about the complaint against Kovac. Pratt comforts Chen.
Abby fears the worst when her brother Eric disappears. Carter and Chen treat a frightened nanny who may have been abused by an employer. Nathan's fellow medics don't appreciate his advice to patients.
Abby's family nightmare continues as she and her mother search for Eric. Corday treats a family who were hit by a truck while out building a snowman and helps the father make a life-or-death decision.
Abby is distressed when her troubled mother Maggie interferes with Eric's treatment. Pratt treats a scared young girl who's been hurt in a car crash. Chen is upset when a baby is abandoned in the ER.
Kovac's troubled life turns tragic when he has a car accident on an icy road and his passenger, medical student Erin Harkins, is seriously hurt. Abby treats a young hockey player with a head wound.
When Pratt is seen bringing a gun into the ER, Carter attempts to defend him. Weaver tries to keep her pregnancy a secret. Romano warns a guilt-stricken Kovac not to make a damaging admission.
Weaver treats a local politician who is brought in after a fall but tests positive for syphilis. Carter is impressed by irascible Dr McNulty, a veteran medic who oversees an inner-city clinic.
Pratt is shocked when his brother Leon asks him to treat a wounded robber who has tricked him into participating in a crime. Carter helps a sickly Dr McNulty and makes a big decision that stuns Abby.
Abby is distraught to learn that her troubled brother Eric has gone missing while flying a plane. Romano receives depressing news. Chen's relationship with Pratt changes radically. Weaver is promoted.
Abby struggles to cope with a multitude of problems. Carter returns from Africa, Weaver confronts a thief, Kovac helps an overdosed teenager and Lewis must deliver grim news to a young cancer patient.
Pratt tries to keep Gallant calm when they are questioned as possible suspects in a murderous rampage at a diner. Carter ponders a life-changing decision. Kovac is forced to consult a psychologist.
Weaver gets into trouble when she agrees to secretly treat her powerful new patron's lover for syphilis. Carter and Abby reassess their relationship. Carter helps a woman who's being poisoned.
Romano expresses his disdain and lack of detailed knowledge of ER procedure, angering everyone around him. Corday's cancer patient must make a choice between her own life or that of her unborn baby.
Abby gets news of her missing brother Eric. Romano continues to make rash decisions - and enemies. Kovac welcomes a fellow Croatian doctor to the ER. Carter guides a group of eager medical students.
Kovac defies the rules to get a dying Croatian boy to Chicago. Despite receiving tragic family news, Carter tries to help a grieving gang member. A baseball player with a heart ailment is treated.
On what is meant to be his last night in the ER, Pratt treats patients including a burned firefighter and victims of a mass cult poisoning, then relays them to Carter's day shift. Romano has surgery.
Carter arrives in Congo as part of a voluntary medical programme, but finds that the tiny hospital he has been assinged to is short staffed and overflowing with patients fleeing the bloody civil war