The quarantine continues. The Angels docs mistrust the DD of the CDC when he shuts them out of the hot zone. Leanne, Ethan, and the CDC doc figure out where the first patient was staying, and head out, hoping to find patient zero. They discover a stolen CDC van along with the patients boyfriend. They try to detain him but he attacks Leanne and she is infected in the scuffle. They find out that the CDC had a vaccine in the testing stages for the virus, but the DD refuses to use it because it hadn't proven effective in animal trials. Ethan goes over his head, and they test the vaccine on Leanne. Unfortunately, it doesn't work. As Elliot, Ariel, and Leanne get worse, Ethan talks the CDC researcher into trying to find a patient with natural antibodies amongst the blood samples they've taken. Just as she's about to give up, they find a match. They successfully transfuse Leanne and derive antibodies for the rest of the patients. The quarantine is lifted, and the ER gets back to it's normal mad crush. As Jesse welcomes a new batch of interns, Leanne heads home to make breakfast for Ariel, who she has adopted.