Twisted Sister is the ninth episode in NCIS Season 4 and also the seventy-ninth episode of the entire NCIS series.
This episode also marks the final appearance to date of Sarah McGee.
A night in for McGee goes wrong when his younger sister shows up at his apartment believing that she might have killed someone. Unwilling to let his sister go to prison, 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.
- Sarah is played by Troian Bellisario, daughter of series producer Donald Bellisario. Troian is the half-sister of Michael Bellisario (who played Chip Sterling in Season Three) and the stepsister of Sean Murray, who plays McGee and despite Sarah's Irish heritage, she cannot handle her alcohol.
- When Abby says that she was going over the trash, the legs of someone, presumbly a man holding a boom mike can be seen walking across her lab.
- This is the second time the team has been called to Waverly University to investigate a dead body, the first being the Season 2 episode, Red Cell (episode).
- The song playing inside the room at Waverly University when Gibbs goes to interview Seaman Jeff Petty's girlfriend, Carolyn is "Tradition" by Living in Question.
- The song playing at the beginning of the episode is "Don't Explain" from the Dexter Gordon album "A Swingin' Affair".
|Leroy Jethro Gibbs||Mark Harmon||NCIS Special Agent in charge of the NCIS Major Case Response Team.|
|Anthony DiNozzo Junior||Michael Weatherly||Senior Special Agent and second-in-command of the NCIS Major Case Response Team.|
|Ziva David||Cote de Pablo||Mossad Liaison to the NCIS Major Case Response Team.|
|Abigail Sciuto||Pauley Perrette||Chief Forensic Specialist, NCIS.|
|Timothy McGee||Sean Murray||Junior Agent of the NCIS Major Case Response Team.|
|Jennifer Shepard||Lauren Holly||NCIS Director.|
|Donald Mallard||David McCallum||Chief Medical Examiner, NCIS.|
|Jeanne Benoit||Scottie Thompson||Tony's girlfriend.|
|Sarah McGee||Troian Avery Bellisario||McGee's younger sister.|
|Samuel Tate||John Cabrera||University security guard and Seaman Petty's killer.|
|Carolyn||April Matson||Co-ed, Seaman Petty's girlfriend.|
|Madison||Katherine Bailess||Co-ed, Carolyn's best friend and head of the cheerleading squad who helped Samuel Tate carry out the crime.|
|Jordan Block||Fidel Gomez||A man who appears in the episode.|
|Cheerleader 1||Kiana Tavasti||Uncredited role.|
|Cheerleader 2||Amber Vasquez||Uncredited role.|
|Cheerleader 3||Tiffany Tynes||Uncredited role.|