Sydney must undergo an extensive lie detector test to satisfy Sloane's frantic search for the SD-6 mole. Meanwhile, with nemesis Anna Espinosa following her every move, Sydney seeks out the connection that a device may have to the 500-year-old prophetic Rambaldi sketch. The mystery of Kate Jones deepens as Will continues to investigate Danny's death; and Sydney discovers that a keepsake from her mother Laura contains more disturbing connections into Jack's past alliances.

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.

Sydney defies her father in her attempt to rescue a kidnapped scientist, while Sloane, seeking revenge, becomes more dangerous than ever. Meanwhile, Francie manipulates an unsuspecting Will for his agency connections.