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An already hectic day at the ER is made even more so when two children are brought in exhibiting symptoms of smallpox. With Weaver (Laura Innes) temporarily unavailable, Carter (Noah Wyle) orders a lockdown at County General to avoid an epidemic -- and avert a nationwide panic. Meanwhile, Lewis (Sherry Stringfield) encounters major problems while trying to get information about a smallpox vaccine from CDC; both Chen (Ming-Na) and Pratt (Mekhi Phifer) appear to have come down with the disease themselves; and a patient riot breaks out, one which may cause the epidemic to spread to the rest of Chicago. This final episode of ER's eighth season ends with a cliffhanger, the ingredients of which include a startling development in the relationship between Carter and Abby (Maura Tierney).