Nadia Santos was the daughter of Arvin Sloane and Irina Derevko, therefore the half-sister of Sydney Bristow. Prior to discovering more about Nadia's identity, she was referred to exclusively as the 'Passenger.' She grew up in an orphanage in Argentina after being taken away from Irina straight after the birth. She worked for the Argentinian authorities and was thought to be a direct link to Milo Rambaldi. Sloane sought her out for her connection to Rambaldi which led to her discovery by Sydney. She subsequently joined APO and began a romantic relationship with Eric Weiss.
Nadia was infected with a compound that turned her into a mindless killing machine during a mission to deactivate a giant Mueller device that floated over Russia. Sloane shot her to protect Sydney, but Nadia did not die and Sloane searched for a cure to save her. He eventually found it and she recovered. When she demanded Sloane choose between her and Rambaldi, he accidentally killed her in the ensuing fight. After her death, Nadia's spirit continued to haunt Sloane.
- Father: Arvin Sloane
- Mother: Irina Derevko (deceased)
- Half-sisters: Sydney Bristow, Jacquelyn Sloane (deceased)
- Niece: Isabelle Vaughn
- Nephew: Jack Vaughn
Before Season 3
She was recruited as a spy from her juvenile detention facility after living a reckless early life. Her training agent told her that she was good at getting in and out of situations without being noticed. Furthermore the fact that she had no family meant that she could not be compromised (Detente).
A close friend and colleague of Nadia's was killed by Roman Vadik. His head was sent back to her office at SIDE, which greatly traumatized her to the point that she could not face confronting Vadik (Authorized Personnel Only, Part 2).
Nadia is discovered by Sydney, Jack and Sloane in Blood Ties. Prior to this, Nadia is exclusively referred to as The Passenger with the Rotunda team initially being lead to believe that the Passenger is a biological weapon to be released by the Covenant.
Nadia joined APO and as she started working with her only family, she realised what she had lost until now. She moved at her sisters house and starts to get along with her and Arvin Sloane. She starts a romantic relationship with Eric Weiss. In one mission, she gets shot and is in a induced coma, until Jack Bristow wakes her up, for he needed information about whereabouts of a terrorist.
Nadia was in the hospital due to her gunshot wound after being shot in the back by her father after she was infected with the stagnant water from the Mueller Device in Russia (Solo). She was unconscious all the time, but during a visit paid by her father, she awoke. After a brief conversation she began to cunvulse and went into a coma once again. Sloane, realizing that Prophet 5 was responsible for her brief conciousness and would give him a Rambaldi-designed drug to cure her if he helped them, decided to succumb to their demands and become a mole within APO for them (Fait Accompli).
Sloane completed all the tasks set by Prophet 5 for him, and when they felt he had sufficiently served his purpose they gave him a syringe filled with a fluid. He turned off Nadia's heart monitor and, after waiting 30 seconds as instructed, he injected her with the fluid. After a brief period Nadia awoke, much to Sloane's happiness (30 Seconds). Nadia was happily greeted by her friends and family after she got out of her coma, but her half-sister was still suspicious of Sloane. Nadia decided to go on a misson with Jack, Renee Rienne, and Thomas Grace to find the whereabouts of Anna Espinosa, as well as to see if Sloane was still aligned with Rambaldi. Even though she found suspicious evidence, she still decided to trust her father (30 Seconds).
The next day, Nadia met up with Sloane at his mansion so that they could talk and connect with each other more. After a brief conversation, Nadia walked into Sloane's office to cut off her bandage from the hospital, but after she did, she found Page 47 -- the Rambaldi manuscript -- underneath one of Sloane's folders. Sloane tried to convince Nadia that he was no longer obsessed with Rambaldi, but Nadia forced Sloane to decide between her or the phophecy. Sloane cried that he didn't want to choose between the two most important things in his life, but Nadia simply threw the page into the fireplace. As the page began to glow, Sloane proceeded to grab the page out of the fire even though Nadia blocked him. In the process, Sloane accidentally pushed Nadia into a glass table, where a large shard of glass pierced her neck and she bled to death (30 Seconds).
Despite her death, Nadia haunted Sloane and warning him about Prophet 5 and what they could do to him. She tried, in vain, to convince him to stop some of his decisions against APO. When Sloane finally got what he wanted -- Rambaldi's endgame, immortality -- Nadia suggested they leave the underground cave that they were in. Sloane casually said they had "all the time in the world", but Jack Bristow entered the cave and, realizing that Sloane was immortal, decided to sacrifice himself and lock Sloane in the cavern for eternity. He detonated a bomb, trapping Sloane under a large piece of rubble. Sloane was thankful that Nadia was there with him, at which point she decided it was finally time for her to leave. The ghost walked away and faded into the wall to the sound of Sloane's cries (All The Time In The World).