After being attacked by a man in the orphanage one night, Nadia ran away and spent her teen years on the streets, committing some 130 criminal acts including assault and petty theft.

In reality, Fox was a rogue agent operating for his own interests and not those of Argentina, a fact Nadia learned during a mission to obtain secret documents during which a close friend and colleague was killed.

For this betrayal, she shot and killed Roberto Fox upon her return from the mission, however (for reasons not explained) the blame for his murder fell upon César Martinez, a fellow operative who, like Nadia, had been recruited from the streets.

She continued working in Argentine intelligence after this event, while Martinez became a freelancer, using the equity of his supposed kill to establish a reputation with criminal organizations.

This triggers a "muscle memory", causing Nadia to write out a complex algebraic equation which, when solved, reveals the coordinates of the Sphere of Life.

Nadia, seeing the madness Rambaldi inspires in Sloane grow as they get closer to the artifact, and after having apocalyptic visions upon touching the Sphere, refuses to retrieve it.

After assisting the newly formed APO unit in rescuing her sister, she accepted a position with the organization, which is a black ops offshoot of the CIA.

Jack led Nadia to believe Irina had been killed by Martin Bishop, a master thief with terrorist connections who had taken Sydney prisoner during an APO mission gone astray.

Nadia shot Bishop to death during the mission to rescue Sydney and continued to fire bullets into him until her gun ran out of ammunition.

In the fourth season, she is shot by terrorist Anna Espinosa and left in a medically induced coma for several days, avoiding a second assassination attempt in the hospital thanks to quick thinking on the part of her father.

In the episode "30 Seconds", Nadia is finally revived permanently when Sloane administers to her a drug designed by Rambaldi, though in order for it to work, he must first kill her (which he does by suffocating her).