Susan Grady is an NCIS polygraph operator. She made her debut appearance in The Inside Man (episode), where she had Timothy McGee retake his polygraph, much to his dismay. It was revealed at the end of the episode that she had him retake his polygraph in an effort to get to know him better, as she had romantic feelings for him.
She reappeared again in Moonlighting (episode), where a private security company she worked for part-time was destroyed in an explosion, and she later revealed that she'd stolen some of the data for personal use. McGee eventually realized that he liked her and attempted to ask her out to dinner, but she turned him down, believing that he was joking, though he insisted he was serious.
After a four year absence, Grady reappeared in the Season 11 episode, Anonymous was a Woman (episode), where she temporarily joined Leroy Jethro Gibbs's team in the field, and was even permitted to interrogate a suspect. It was revealed later in the episode that she was undergoing training to become a criminal investigator, with intentions to apply for a position in San Diego.