S04-E01 :: "Authorized Personnel Only (Part 1)" :: Original Airdate: 01.05.05
Sydney, Vaughn, Jack and Dixon get a new boss, Sydney and Vaughn question whether they'll ever be able to reconcile their relationship, Sydney learns a terrible secret about her father, and Nadia is reluctant to return to the spy world since learning the truth about her father.
S04-E02 :: "Authorized Personnel Only (Part 2)" :: Original Airdate: 01.05.05
S04-E03 :: "The Awful Truth" :: Original Airdate: 01.12.05
To learn the location of a stolen NSA code-breaker, an undercover Sydney must convince a murderous arms dealer to fall in love with her. Meanwhile, Vaughn fears that Weiss might have been killed on a mission, and Sydney and Jack argue about telling Nadia the horrible truth about her mother, Irina.
S04-E04 :: "Ice" :: Original Airdate: 01.19.05
Sydney goes undercover as an earthy social worker and Vaughn as a lascivious, semi-tipsy priest to track down a deadly new bio-weapon. Meanwhile, Sydney is frightened when Vaughn's inner-demons regarding deceased wife Lauren come to the surface, and Nadia turns to a reluctant Jack to learn truths about her mother.
S04-E05 :: "Welcome to Liberty Village" :: Original Airdate: 01.26.05
Sydney and Vaughn pose as a married couple in suburbia to track down a weapon that could send society back to the Dark Ages, only to find that marriage is a strain on their relationship and the community is not as innocuous as it appears.
S04-E06 :: "Nocturne" :: Original Airdate: 02.09.05
Vaughn and Jack search for a cure when Sydney is infected with a mind-altering and potentially deadly hallucinogen, causing her to slowly lose touch with reality.
S04-E07 :: "Detente" :: Original Airdate: 02.16.05
Sydney and Nadia argue about Sloane, who worries about Nadia as she and Sydney go under cover as wealthy, irresponsible young heiresses to reveal a hidden deadly chemical.
S04-E08 :: "Echoes" :: Original Airdate: 02.23.05
With Nadia's life on the line, Sydney must race to bring down former nemesis Anna Espinosa.
S04-E09 :: "A Man of His Word" :: Original Airdate: 03.02.05
Vaughn agrees to a despicable request from Sark involving Lauren's buried corpse, so that he will help Vaughn and Sydney track down Anna Espinosa and save Nadia.
S04-E10 :: "The Index" :: Original Airdate: 03.09.05
Sydney's theory that Sloane is trying to re-form the Alliance jeopardizes her relationship with Nadia, who refuses to believe that her father could be double-crossing the CIA.
S04-E11 :: "The Road Home" :: Original Airdate: 03.13.05
Sydney inadvertently places an American civilian in jeopardy while on a mission in Germany.
S04-E12 :: "The Orphan" :: Original Airdate: 03.23.05
Nadia fails to disclose her tainted past with a man who is the focal point of the agency's mission, putting her, Sydney and Weiss in grave danger.
S04-E13 :: "Tuesday" :: Original Airdate: 03.30.05
When a mission goes awry, endangering Sydney's life, Marshall is the only one who can help.
S04-E14 :: "Nightingale" :: Original Airdate: 04.06.05
While searching for the truth about Vaughn's presumably deceased father, Sydney and Vaughn put their lives and careers on the line.
S04-E15 :: "Pandora" :: Original Airdate: 04.13.05
Sydney's aunt, Katya Derevko, gives her devastating news; Vaughn steals a device to use as a bargaining tool in order to learn more about his father.
S04-E16 :: "Another Mister Sloane" :: Original Airdate: 04.20.05
Sydney must work together with Sloane in order to catch the man who has been impersonating Sloane.
S04-E17 :: "A Clean Conscience" :: Original Airdate: 04.27.05
Sydney and Nadia learn that Sophia, the head of the orphanage that cared for Nadia as a child, was badly beaten, and when Sloane learns why she was beaten, he fears for Nadia's safety.
S04-E18 :: "Mirage" :: Original Airdate: 05.04.05
S04-E19 :: "In Dreams..." :: Original Airdate: 05.11.05
The mysterious man who has been impersonating Sloane resurfaces, and he is hot on the trail of Rambaldi; shocking revelations about the real Sloane come to light, making everyone question his true intentions.
S04-E20 :: "The Descent + S04-E21 Search & Rescue" (2 HOURS) :: Original Airdate: 05.18.05
An agent's life hangs in the balance as the team races to track down Nadia's childhood caregiver, Sophia; Jack, Sydney and Nadia learn that Irina Derevko is alive.
S04-E22 :: "Before the Flood" :: Original Airdate: 05.25.05
Only Sydney, Jack, Irina, Vaughn and Nadia can save the world from the plan put into motion by Elena Derevko; the Rambaldi prophecy regarding Sydney and Nadia comes one step closer to being reality.