|One to Go|
|Original Airdate||January 15, 2009|
The CSI team works to close Grissom's last open case, the "Dick & Jane" murders, as Grissom prepares to leave the team for good. Before leaving, Grissom offers Dr. Raymond Langston, who helped the CSI's with the "Dick & Jane" case, a permanent position as part of the CSI team.
Picking up where "19 Down" left off, Brass identifies the new victim found under the bridge as Jeffrey Masters. His wife Maureen is missing, and Brass estimates that the team only has at most 48 hours to find her alive. After the Sheriff is briefed by Brass and Ecklie, Ecklie, who is slated to step into the Undersheriff position, tells Grissom that the sheriff has personally requested he stay on until the conclusion of the case. Continuing to work with Dr. Ray Langston, the professor whose class Nathan Haskell was speaking to from jail, the CSIs focus on what drugs Haskell might have used to subdue his male victims. Positing that Haskell had an accomplice in Langston's class, the CSIs also turn their attention to Langston's students. Brass speaks with Dan Forrester, the student who suggested getting a serial killer to talk to the class and corresponded with Haskell, but when he realizes he is a suspect, Dan tells the detective the idea came from multiple students in the class. The team visits Langston's classroom and plays the video of Haskell speaking to the class, trying to pinpoint if he made eye contact with any of the students during key comments. They zero in on a student named Thomas Donover, who asked Haskell how he controlled his victims and was told where to dump Jeffrey Masters. The police find him missing when they go to his house, and his wife Kelly insists that she does not know where he is. The CSIs search the Donover house and Greg finds shoes that match the treads found at the scene of Ian Wallace and Justine Stefani's murders. Tom is definitely the accomplice. While Tom torments Maureen, the CSIs race to isolate the location of the house where Haskell took his victims—and where Tom likely has Maureen now. Hodges discovers a kind of moss on Tom's shoe that narrows their search to the north side of Lake Mead, but that still leaves the CSIs with a lot of ground to cover and not much time in which to do it.
Nick finds a box of video tapes in Tom's house—but no VCR around and recalls that Gerald Tolliver had a VCR but no tapes. Kelly confirms Tolliver was a friend of her husband. Catherine finds sage extract at Tom's house that Henry confirms could have been used to subdue Haskell's male victims. A print leads them to the dealer, but he's killed accidentally when he runs from the police. Nick views the videotapes and see Haskell's first victims, Joel and his fiancée Tiffany, with Tom Donover and Gerald Tolliver—and later with Haskell. Grissom consults star charts hoping to find a way to identify the location of the house, while Langston pays Haskell a visit in jail, hoping to get the information out of him. He tries to trick Haskell into thinking they already have Tom and Maureen and just want the location of the bodies of his female victims, but Haskell sees right through his ruse and gives him nothing. Grissom uses the moon in the videos to find the house's location and discovers it is in Black Mesa. Brass and his team rush there and Tom is killed by a shot to the head just as he is about to murder Maureen. Brass frees her and the CSI team canvasses the house and Grissom discovers the bodies of Haskell's female victims under the floorboards of the house. The case closed, Grissom visits Langston at WLVU and suggests he apply for the new vacancy at CSI. Grissom finishes packing up his office, and despite an impassioned plea to stay from Hodges, exits CSI, catching only Catherine's eye as he walks past the team hard at work. Grissom heads to Costa Rica where he reunites with Sara Sidle, kissing her passionately.
- William Petersen as Gil Grissom
- Marg Helgenberger as Catherine Willows
- George Eads as Nick Stokes
- Eric Szmanda as Greg Sanders
- Robert David Hall as Dr. Al Robbins
- Wallace Langham as David Hodges
- Lauren Lee Smith as Riley Adams
- Paul Guilfoyle as Jim Brass
- This episode marks the last official appearance of Gil Grissom, who manages to track down Sara Sidle in Costa Rica.
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