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.

With the aid of Katya Derevko and CIA imprisoned security systems designer Toni Cummings, Sydney and Vaughn attempt to track down Sloane and Nadia. But Lauren and Sark are also in hot pursuit of them in order to uncover the secrets of Rambaldi. Meanwhile, Vaughn's obsession with tracking down Lauren is beginning to consume him. During a mission to Cuba to uncover more Rimbaldi findings, Sydney and Vaughn turn the tables on an old foe; the Taiwanese scientist and torturer "suit and glasses. Also, Katya expresses her attraction to Jack.

Lauren stages a stunning betrayal by impersonating Sydney and blowing up the CIA offices to steal classified materials, and nearly killing Marshall in the process. But Sark is captured during Lauren's escape, and Sydney decides to play the impersonating game herself to learn where Laura is heading off too. Meanwhile, Vaughn comes face to face with his darkest demons in pursuit of his traitorous wife. Nadia must decide whether or not she can trust her father, Sloane, in the pursuit of Rambaldi's most priceless artifact and escape from CIA custody. During a mission to South Africa at a Rimbaldi artifact dig, Sydney has a some help and hindrance from Katya Derevko, as well as a final one-on-one fight with Lauren. Afterwards, Sydney receives a shattering revelation from Lauren that will make her question everything (and everyone) she thought she could trust.

On his own and desperate to find out more about his supposedly-dead father, Vaughn is pressured into a rogue operation for an unknown organization in exchange for information on the whereabouts of his father. He gains more than he bargained for in the deal. Meanwhile, Nadia is meeting with her aunt, Katya Derevko, in order to learn more about her mother, but Sydney doesn't trust Katya's motives.

After a tactical group infiltrates the DSR and steals all the Rambaldi artifacts, CIA director Hayden Chase discovers that the alarms at the DSR were disabled from Nadia's computer, allowing the raid to happen. Mrs. Chase shows up at the apartment to question her. Soon Sloane and Jack arrive and suspect that Sophia, who had access to the computer while she was living with Sydney and Nadia, is in fact Elena Derevko. They follow her trail to a dead Rambaldi follower, a stunning betrayal, and a presumed dead family member when in a surprising twist, Sydney and Nadia learn that Irina Derevko is in fact alive.