Twisted Sister is the seventy-ninth episode of NCIS and the ninth episode in Season Four. This episode also marks the final appearance of Sarah McGee.
When his younger sister shows up at his apartment in the middle of the night, believing that she might have killed someone, McGee takes matters into his own hands and risks his NCIS career as he attempts to find out what happened while the rest of the team investigate the death of a Navy sailor and as it turns out, the victim is connected to McGee's sister...
Sarah McGee returns, asking for her brother's help as she believes that she might have killed someone.
The team discover that McGee's become an author and has published a book titled Deep Six.
McGee later resigns from NCIS but Gibbs soon talks him into changing his mind and he remains on the team.
Tony first saw Sarah's picture on McGee's iPod in the Season 3 Episode 16, Family Secret (episode). He was unaware of her identity but insisted that she had to be McGee's sister since she was too attractive to be his girlfriend.
This is the episode which reveals the secret behind McGee's mysterious new wealth, hinted at in several earlier episodes of Season Four.