Sean Walker stumbles into a national conspiracy after his fiancé mysteriously disappears from a Caribbean cruise.

The president's staff grapples with a new reality; the conspiracy engulfs an FBI agent and a mercenary with questionable ties; a shadowy figure emerges with knowledge of the detainees.

The administration unveils a tough new strategy to force Sophia to reveal the detainees' plan; Vicky and Carter possess a crucial hostage.

The White House must deal with a mysterious biological threat; Carter and Vicky keep their hostages alive while waiting for more instructions; FBI Agent Collier discovers Vicky's secret life.

The CDC tries to identify the contagion and treat those infected as the biological threat intensifies; Simon asks Sophia to betray Thomas.

Sean encounters a mysterious conspiracy theorist while looking for answers in Leila's home; Simon's allegiances are tested.