Alias - Season 3 Episode 12 -

Jack contacts a mysterious woman, that of former KGB agent Katya Derevko, Irina's older sister, to help him free Sydney and Vaughn, whose plane has crashed inside North Korea while seeking to find a defecting Russian scientist, named Leonid Lisenker, whom Sark is trying to kill before turning himself to the CIA. But Jack is faced with a curious conundrum when Katya tells him that she will not put the rescue plan in motion until he fulfills a favor: assassinate Sloane.