Sydney discovers a terrifying secret when she's sent on a case to track down a new generation of weapons. Meanwhile, Vaughn suspects Jack of setting up Sydney's mother to take a fall. Sloane tells Jack the truth about Emily's death.

Sydney's trust in her father begins to fade. Meanwhile, Sydney and Vaughn may have been exposed to a deadly virus while in Taipei; Sloane haunted by Emily's death begins to unravel. Vaughn enlists Will to help research a case.