Experts from the Centers for Disease Control, New York Police Department and FBI respond to New York City's first biological attack since 2001: anthrax. Then, the CDC detects an illness affecting young girls across the US.

The CDC, US Army and a Bronx Zoo veterinarian join forces to identify a disease that is rapidly filling the city's emergency rooms and killing 17,000 crows and zoo birds in New York City. Then, a virus tears through the Southwest.

Patients that received organs from one donor exhibit bizarre behaviors before lapsing into comas. Then, in the Midwest, a mysterious and terrifying pox outbreak leaves more than 70 patients plagued by strange, pus-filled lesions.

Violent, flu-like symptoms strike down men in the college town of Fort Collins, Colorado. Then, an elderly woman who recently returned from China is rushed to a Northern Virginia hospital.

Hundreds of injured soldiers returning from the Middle East bring back incredibly powerful mutant bacteria. Then, the CDC is flooded with reports when an invisible assassin causes severe illness in children across the US.

After a huge earthquake hits California, a deadly fever spreads quickly, likely caused by a fungus released during the disaster. Then, a horrendous bacterial outbreak forces one of the largest food recalls in US history.