Jack takes drastic measures to ensure that the NSC never finds out the truth about Sydney's murder of a Russian diplomat. But his actions place a heavy strain on Vaughn's marriage, as Lauren gets closer and closer to the truth about Sydney. Meanwhile... (more), Sydney agrees to go on a mission with Sloane in order to thwart plans to obtain the operating system to a deadly weapon -- and she discovers an unlikely ally in the hunt for her missing two years.