The fictionalized and completely glorified version of the CIA operates across the world with impunity, Sydney Bristow disabling (she rarely used a gun in the beginning) people as she pleases. She is tricked into to joining SD-6, a terrorist organization under the guise of the CIA. When her fiance is killed by them, she joins the real CIA, meeting Michael Vaughn. She acts as a double agent along with as she later discovers, her father Jack. The head of SD-6, Arvin Sloane, is obsessed with an inventor, Milo Rambaldi, a da Vinci like character who created magnificent with very limited materials and technology. This provides the backdrop for high tech infiltration and theft of these artifacts, and the discovery of these objects with unique properties.
Sydney's coworkers at SD-6, her partner Marcus Dixon, and Marcus Flinkman, the tech guy, are oblivious that they are not working for the real CIA, and Sydney finds it hard not to tell them.
To balance it out, her friend's Francie and Will both thinks she works for the bank Credit Dauphin, the cover for SD-6, so Sydney has to constantly lie to them about her whereabouts and activities.