With two suspects in question, Ryker’s own beliefs about the case are tested.

In Florida, a man mysteriously falls ill and dies. Special Agent Matthew Ryker suspects an anthrax attack - how many others have been infected?

Ryker’s investigation moves to New York as another case of anthrax occurs. Bruce Ivins begins having suspicions of his coworkers.

The FBI learns more about Bruce Ivins’ peculiar past behaviors after an old colleague raises red flags. Ryker and Dani trace the origin of the letters.

All eyes shift to “Mr. Z.” As they start to zero in on a suspect, Ryker and Dani get new assignments - but that won’t stop them from chasing their lead.

An attack on Capitol Hill sends Ryker and his team to a mail facility that’s become a hot spot for anthrax infections.

An employee at the monkey research facility falls ill, causing Dr. Nancy Jaax to fear the virus has spread to the human population; Jerry Jaax searches for a way to protect his wife; Dr. Wade Carter is obsessed with exposing the dangers of Ebola.

A volatile situation inside the research facility comes to a head; Dr. Jaax steps up, but exhaustion threatens the precision needed to sterilize the threat; the press arrives, and neighbors become aware of the danger next door.

When representatives from varying agencies disagree on how to handle Dr. Nancy Jaax's discovery, she realizes there are few protocols in place for containing a deadly virus on U.S. soil; an employee at the monkey research facility falls ill.

Dr. Nancy Jaax works tirelessly to find out why the virus is behaving differently than expected in human victims; unforeseen dangers arise at the research facility; Jaax is forced to make a choice between her family and her duty to her country.

Dr. Nancy Jaax and her lab partner, Dr. Peter Jahrling, must take matters into their own hands to determine the source of the virus before it spreads; Dr. Jaax convinces an employee to hand over samples from infected monkeys.

Dr. Nancy Jaax has one of the most dangerous jobs in the world handling deadly viruses; after a lab accident, she is faced with a possible Ebola outbreak on U.S. soil.