Vaughn uncovers evidence that indicates Sydney's father may have been responsible for the deaths of more than 12 CIA officers.
Sydney finds trouble in the form of her arch nemesis while in Madrid to retrieve a 500-year-old sketch, and Will investigates Danny's death.
Vaughn unexpectedly gives Sydney a Christmas gift, Jack must save Sydney's life when she is suspected of being the SD-6 mole and the order has been given to torture and kill her, and Will begins to research SD-6.
Sydney accidently gives SD-6 access to a nuclear weapon, forcing her to head to Cairo and take on a dangerous foe, and Will questions the circumstances surrounding Danny's death.