Two couples finish a gourmet meal in a sleek, modern apartment. They're newly acquainted and the hosts don't notice the psychotic grimace on their guest's face, or that he pours a powder in their drinks. Shortly after the hosts become woozy from the drugs, the cellist smashes a decanter of booze over the man's head and throws him through the glass coffee table.
Cut to Willows in the office. Her call wakes Langston from a fitful sleep. Does some telepathy tell him it's his ex-wife Gloria and her current husband Phil who are in danger. Willows reports a body found in Los Angeles. Looks like the CSI team is leaving Las Vegas. It's not clear why they're interested until they get to the crime scene. The victim, found in a Dumpster, has 12 post-mortem stab wounds – a sure sign of the twisted work of escaped serial killer Nate Haskell. And the victim is Langston's ex-wife's husband.
Willows and Langston rush over to the apartment, where a bit of evidence is left specifically for Langston's benefit. On the counter is a gift-wrapped box with a note, some sheet music, and the engagement ring he once gave to his ex-wife. Haskell enjoys nothing more than taking from someone what they love most.
Knowing that his ex is probably dead, Langston quits the case and heads back to Vegas, where he gets drunk and leaves a message for his team at the office that the one person he loves is gone and there's only one thing left for him to do.
Willows and the LA CSI continue to investigate the murder scene. Security camera footage from the parking garage shows Haskell and his new wife, Tina Vincent, driving away in Phil and Gloria's car. LAPD finds the car abandoned with blood in the trunk, but no body. They determine that the blood comes from only one victim. Meanwhile, LAPD is searching the Willoughby Observatory, which was pictured on a postcard left at the crime scene. Willows worries that Langston will go after Haskell. All the clues suggest Haskell is provoking Langston.
Langston tracks down Tina and physically restrains her. Later LAPD finds her dead and tied up. She was obviously tortured. LAPD suspects Langston, but the Vegas team thinks Haskell is the culprit.
Nick shows up at his hotel, where Langston explains that he did have a confrontation with Tina when he tried to get information, but he didn't kill her. Nick tries to convince Langston to get a grip because Haskell is obviously framing him so that he becomes isolated from his team, thus rendering him more vulnerable prey.
A ticket at the crime scene leads Nick and Langston to a carnival, where they find Haskell on a carousel. They try to apprehend him, but LAPD shows up and botches their efforts. Right before LAPD cuffs Langston for brandishing a gun, Haskell shouts from the carousel that Gloria is still alive.
The LA detective is upset that Langston had the info to find Haskell but went of on his own and put his LAPD men in danger. He insists Langston has to go back to Vegas. Catherine agrees. The rest of the team remains in LA in pursuit of Haskell.
CSI Brody finds forensic evidence suggesting Haskell is hiding out in an industrial building and this could lead to his location. Back in Vegas Ray lands at the airport and Robbins picks him up. Ray convinces Robbins to take him to the Office where Ray finds out he no longer has privileges for the network. He coerces Hodges to use his password and gets to work. The key comes from the story of Willoughby J. Willoughby, a wealthy philanthropist who married twice and shot his first wife in the head. The Vegas team (Greg, Langston, Hodges)find out that the second wife was admitted to a psychiatric hospital and died there. They believe that the 'industrial building' in question may be that hospital. Greg leaves to call Willows to inform her about this. The LAPD team goes to the old hospital, and sure enough it's the spot that Nate has been holding up. There's a lot of blood and a wrapped up bundle under the sheet, but no Gloria.
Langston sends Hodges on a fool's errand and following the historical trail, he makes an amazing discover regarding Haskell's identity – he's the grandson son of Willoughby's second wife. He determines the killer is likely hiding out at an old abandoned Victorian house belonging to Haskell's dad - same farmhouse from the Father of the Bride (1). Langston goes off on his own to the farmhouse. Langston finds a dying Thorpe (Willoughby's son, Nate's father)and finds Gloria chained up in a room. As he tries to free her, Haskell walks in holding a gun. "Welcome home, Ray," he says. To be continued!