Sydney Bristow is a college student who leads a double life: she works for shadowy government agency called SD-6 which is supposed to be a covert branch of the CIA and reports to Arvin Sloan. Recently engaged, she tells her boyfriend, Danny Hecht, the truth. The next day, he is murdered. Later, Sydney's father, Jack Bristow, tells the truth: he is a double agent for the real CIA, as SD-6 is a renegade agency who allegedly killed Sydney's fiancé. Sydney must make a decision which will haunt her for the rest of her life. Sydney's partner in the field, Marcus Dixon, is also unaware about his true alliances as is SD-6's tech expert, the socially awkward Marshall Flinkman. Sydney's friends, the headstrong Francine, and the ambitious journalist Will Tippin are also unaware about Sydney's double life, until Will becomes inquisitive about Sydney's well-being following her fiancé's murder.