Syd learns she's pregnant by Vaughn, who's suspected of being a double agent. Dean: Tyrees Allen. Parks: Art Chudabala. Lehman: James Russom. Curtis: David Marshall Grant.
The murder of a close friend leads Sydney to join with CIA fugitive Renée Rienne to find the killer; Jack enlists a reluctant new agent (Balthazar Getty); and Weiss considers a promotion that would take him from his colleagues. Doctor Lynn: Kathe Mazur. Ahern: Kevin Cooney. Lars: Christian Gill. Roemer: Larry Cedar. Renée: Elodie Bouchez. Weiss: Greg Grunberg. Jack: Victor Garber.
Sydney teams with Grace to track Rachel, who's suspected of being a traitor; and Sloane is granted time to obtain a possible cure for Nadia. Kelly: Amy Acker. Dolzhenko: Jack Laufer. Dean: Tyrees Allen. Walsh: David Pressman. Rachel: Rachel Nichols. Sloane: Ron Rifkin. Dixon: Carl Lumbly.
Syd's life is endangered when Dean learns that Rachel is still alive; Sloane awaits the outcome of his sentencing. Kelly: Amy Acker. Dean: Tyrees Allen. Pierpont: Rowena King. Walsh: David Pressman. Harkin: Stephen Spinella. Rachel: Rachel Nichols. Sloane: Ron Rifkin. Jack: Victor Garber.
Syd and Grace run into mercenaries who are after the cryogenic container Renee stole; Sloane takes action to get reinstated into APO and to continue his search for a cure for Nadia. Renee: Elodie Bouchez. Senator Lewis: Jennifer Hetrick. Luc: Patrick Bauchau. Dean: Tyrees Allen. Keach: Joel Bissonnette. Grace: Balthazar Getty.
Syd guides a nervous Rachel on her first solo mission; Sloane's deal with Dean requires him to betray his new-found trust with APO. Kelly: Amy Acker. Nicole: Jordan Claire Green. Dad: Ian Patrick Williams. Vak: Ron Bottitta. Eric: Trevor Duke.
Syd and APO try to learn for whom Dean is working and what their plans are; the group claiming to have a cure for Nadia plays games with Sloane. Nadia: Mia Maestro. Kelly: Amy Acker. Dean: Tyrees Allen. Choy: Keone Young. Ehrmann: Angus Macfadyen.
Syd and Rachel team with Sark to keep a bomb from a mercenary; Jack and a former lover---an MI-6 agent---are captured. Sark: David Anders. Elizabeth: Caroline Goodall. Masari: Ntare Mwine.
Syd is reunited with Vaughn after being kidnapped and hypnotized by a familiar face, who has a vested interest in her future---and in her unborn child.
Sydney's colleagues need Weiss' help to infiltrate the CIA after her distress call is disrupted; Jack sets up a meeting to ferret out a traitor.
Irina teams up with Jack and Sydney to hunt for “The Horizon” in a Vancouver bank.
New mother Sydney is back on the job ahead of schedule when Will (Bradley Cooper) is kidnapped by Anna; Sloane's odds of finding a cure for Nadia improve. Anna: Gina Torres.
Prophet Five's cure for Nadia sounds less promising to Sloane than he originally thought; Anna Espinosa is still missing; Renee mulls a job offer from Sydney; and Rambaldi's Page 47 gets another look. Ehrmann: Angus Macfadyen. Nadia: Mia Maestro.
Sydney's ongoing feud with Anna takes a new turn when a strange computer chip is found inside Renee; Sloane's association with Prophet Five begins to take its toll. Vaughn: Michael Vartan. Nadia: Mia Maestro.
An undercover Sydney works with Sark (David Anders) to beat Prophet Five to a crucial element in Rambaldi's prophecy; Vaughn sees his daughter for the first time; and Rachel learns what Thomas has been hiding. Korman: Perry Wolberg.
In the series finale, Sydney and Vaughn go after Sloane, who has kidnapped Marshall and Rachel as well as teamed up with Irina to see the Rambaldi prophecy through. Sark: David Anders. Irina: Lena Olin. Francie: Merrin Dungey.