Dr. Carter, Abby and other staff of the ER are quarantined as the CDC investigate a mysterious, deadly outbreak.

Abby's family nightmare continues as she and her mother Maggie search for Abby's missing brother Eric, who Abby suspects is suffering from serious mental problems. Meanwhile, Corday treats a family of patients who, while building a snowman, were severely injured after being struck by a truck driver.

Dr. Romano seizes control of the ER and manages to offend everyone. Dr. Kovac asks Dr. Corday's help in the quest to bring a sickly Croatian boy to the U.S. for medical treatment.