Sidney Bristow is a college student who has an unusual job – she is a spy working for the CIA under secret conditions where not even her friends knows what she does. When her boyfriend proposes Sydney tells him what she does for a living and her employers kill him in line with procedures. Deciding to leave the agency before they kill her too Sydney discovers that she has actually been working for SD6, an agency that is actually a shadowy criminal organisation world-wide. Sydney joins the CIA and works as a double agent to help CIA Agent Vaughn to bring down SD6. She finds that her father is the other double agent within SD6 and the pair work together. While following her missions to uncover the work of the prophetic Rambaldi she must feed information back to the CIA without blowing her cover. Sydney Bristow是政府秘密分支机构SD-6的情报员，但是她的男友带来了杀身之祸，雪梨在向SD-6的长官求证后，发现男友正是死在SD-6的手下，同时她发现SD-6实际上是反政府的机构。Sydney加入了CIA成为一个双面间谍，也就是说她在完成SD-6分派的任务的同时，将任务的细节情报汇报给她CIA的上司，Vaughn....