In the season finale, Chicago residents become fearful of an epidemic. When Carter and Abby treat two children with ominous symptoms, the emergency room is placed under quarantine until disease experts from the federal government can arrive. As Carter fights to save the youths, the staff is trapped with the suffering patients and a busload of injured and irritable senior citizens. Reporters surround the hospital, and police block the exits, prompting the restless victims to stage a minor riot in an attempt to escape the dangerous and stifling conditions inside. Meanwhile, Pratt (recurring guest star Mekhi Phifer) and Chen--who may have contracted the disease--ignore their own symptoms as they labor to save the life of a homeless man, Stan the Can (recurring guest star Harrison Page), who is a frequent patient at the hospital.