Sydney Bristow is a college girl who leads a double life. While she continues her education at college she is also a spy.
Originally thinking she was working for a special department in the CIA, Sydney comes to realise she is in fact working for SD-6, the very enemy which the CIA is fighting against. After realising this she walks into the CIA headquarters at Langley and reveals everything, turning herself into a double agent.
She is now striving to bring down SD-6 from the inside with the occasional help of a man she hardly knows who is also a double agent inside SD-6, her father..