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.

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