The usual chaos at County General quickly goes from frenzied to frightening when two children are brought in with symptoms eerily similar to smallpox. Racing to stem a possible plague - and national panic - Carter immediately orders an ER lockdown, with Weaver outside and a waiting room full of anxious patients inside. As Lewis attempts to contact the CDC about a vaccine, one patient's condition continues to deteriorate, while two of County's newest residents begin to show symptoms of exposure.