Derek Stillwater, bioterrorism expert for the Department of Homeland Security, already has his bags packed for vacation when he gets the call: "Sarin gas attack on a Detroit restaurant. Fifty-two dead." The killer calls himself the Serpent and demands three million dollars. If he is not paid on time, more people will die.Special Agent Jill Church is assigned to keep tabs on Stillwater. While the FBI brass are playing politics with the press, Stillwater and Church discover a disturbing link to a cult responsible for the sarin attacks on a Japanese subway.Furious at Stillwater's unorthodox methods, the FBI demands his immediate arrest. Now suspended from the case, Church knows that she and Stillwater are the only ones who can stop the Serpent from releasing sarin gas at a concert. 21,000 lives are at stake–including her own son's.