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.
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.
Vaughn uncovers evidence that indicates Sydney's father may have been responsible for the deaths of more than 12 CIA officers.