In the episode, Leroy Jethro Gibbs is visited by Maddie Tyler, the childhood best friend of his deceased daughter, for help in stopping a Marine who she believes is stalking her.
It is later revealed the stalker is using Tyler's home to get their hands on four million dollars in stolen Iraqi aid money.
"Requiem" was originally intended to be the 100th episode of the series, until the producers switched the order with "Chimera" because they believed it would be suitable to air near Halloween.
The episode begins with Special Agent Anthony DiNozzo (Michael Weatherly) shooting two armed suspects at a dock before diving into the water to save his superior Leroy Jethro Gibbs (Mark Harmon) and a young woman from a submerged car.
After returning to NCIS he, DiNozzo, Timothy McGee (Sean Murray) and Mossad liaison officer Ziva David (Cote de Pablo) initiate an investigation on Haas.
Following an autopsy, Medical Examiner Donald Mallard (David McCallum) confirms that Haas was murdered sometime before Tyler's kidnapping, meaning somebody else took her.
Throughout the case, NCIS Director Jenny Shepard (Lauren Holly) believes Gibbs has become personally involved because of his relationship with Tyler.
Meanwhile, the rest of the team discover that Haas was not, in fact, stalking Tyler, but instead was using her apartment as an accommodation address, waiting for a letter he posted from Iraq with details leading to the location of the four million dollars.
Returning to Tyler's apartment, Gibbs receives Haas' letter and retrieves the money, shipped from Iraq disguised as the "personal effects" of a K.I.A.
"[1] In introducing the character of Maddie Tyler, Brennan wanted to show what it would be like if Gibbs saw a girl who may have well been his daughter if she lived, and then put her into jeopardy.
While shooting in San Pedro, Michael Weatherly was allowed to run up to the water, but a stunt man later stood in to perform the dive.
Body doubles were on hand, but the producers were so impressed by how Harmon played dead, they felt one was not needed, as they believed one could not replicate the performance.
[3] In total viewers, "Requiem" easily won NCIS and CBS the 8 p.m timeslot; the Fox crime drama Bones, which drew second, was seen by around half the audience.
"[6] Julian Spivey from Examiner.com included "Requiem" in his compile of the "10 greatest episodes of 'NCIS'" in January 2012, saying, "Every fan of NCIS knows the tragic story of Gibbs' wife and daughter and it's a storyline that pops up at least once a season.
Because she was close to his daughter he'll do everything to protect her and this almost results in his death in one of the show's most entertaining and heart pounding scenes in which Gibbs and the girl are submerged in a car underwater.