Sydney gets shocking info on her dad's role in Danny's murder and takes on a countermission against the SD-6 to bring down an arms dealer linked to a missing nuclear weapon. Meanwhile, Will begins to grow suspicious of his friend's secret life; and Vaughn is taken off Syd's case after his mishap puts the entire world in danger.

A mission to steal an ancient sketch pits Syd against her sworn nemesis, a Russian agent who's after the same target. But when the container holding the painting proves impenetrable, the two foes are forced to team up to satisfy their respective agencies. Meanwhile, Will begins to notice something very fishy about Danny's murder; and Francie frets over her guy's possible infidelity.

Sydney briefs her CIA handler, Agent Vaughn, on her recent captivity at SD-6 and is surprised when he unexpectedly gives her a Christmas gift. Meanwhile Jack has to find a way to save Sydney when he discovers that Sloane has ordered her tortured and killed for being the suspected SD-6 mole. Will may be making the mistake of his life when he begins to research a name heard on a mysterious audiocassette -- SD-6.

Sydney is grateful and proud of her father after he saves her life while on a case in Havana. But her admiration is short lived when Vaughn discovers further evidence that Jack may have been responsible for the deaths of over a dozen CIA officers many years earlier.