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

On a busy Halloween night, Carter and Abby are the only staffers in costume when victims of an apartment building fire pack the ER. Corday takes on a new med student for a surgical rotation - Paul Nathan, who suffers from Parkinson's disease and decided to pursue medicine after being diagnosed. Despite a difficult first day, both professionally and medically, Nathan makes a difficult diagnosis. Romano's rehab lags behind his expectations, and he begins to think his role in surgery is no longer an option. In a moment of personal weakness, he tries to express his feelings for Corday. Weaver continues to display erratic behavior, raising staff suspicions about her menopause. Luka's burgeoning sex addiction worsens, as an affair with Chuny is revealed, and tensions rise when he treats a patient with a perpetual erection.

It's Greg Pratt's last shift at County General and he treats a number of cases that were started by John Carter on the day shift. They treat a 12 year-old near drowning victim who has little chance of recovery; a Buddhist nun who has a special gift of seeing another's inner self; a woman who is convinced that the day's solar eclipse signals the end of the world; a drug addict who scams both of them for pain medication; and a pregnant woman who had her baby torn out of her womb. Dr. Romano has his re-attached arm amputated. Carter receives a call from Luka Kovac asking if he can come to the Congo and help out. Abby is none too pleased. Meanwhile, Doc Magoo's burns to the ground.

Weaver contemplates hip replacement surgery after she finds it hard to do her labor-intensive job. Meanwhile, Kovac tries to ease Abby's fears about raising a child together. Neela decides to attend a support group for military spouses but when she offers her opinions on the war, the meeting turns into a debate. And after Sam treats a fainting victim, she finds herself with an intriguing job offer.