Gil Grissom is the supervisor of the graveyard shift of Las Vegas' elite crime scene investigators. Holly Gribbs, fresh out of the academy, joins the team. Jim Brass is head of the unit and is trying to scare Gribbs from CSI. Catherine Willows, mother of a young daughter, is the number two CSI on this shift. Warrick Brown and Nick Stokes are competing to solve their 100th case to earn a promotion to CSI 3. Grissom investigates a murder staged to look like a suicide with precious little evidence. Warrick and Catherine take the case of a drunk who breaks into the house where he had been staying and is shot to death. Nick talks to a man who picked up a woman who drugged and robbed him.
Catherine violates department protocol when she takes the case of a rape accusation against her ex-husband. Warrick and Sara search for the missing bullet that will either exonerate or indict a cop for murder. Grissom and Nick investigate when a female skeleton is found buried in cement under a house.
Grissom's nemesis, serial killer Paul Millander, reappears and claims a third victim in this gripping episode. The latest slaying matches Millander's previous killings in that it recreates his father's murder. The killer's next target was born Aug. 17, 1956...which just happens to be Grissom's birthday.
Grissom and his crew handle their highest profile case to date when the city's former chief of detectives is slain execution-style in his house following a wild party. Missing from the residence are the chief's trophy wife and their 7-year-old daughter. Catherine and Warrick follow the trail to Miami, and soon enlist the help of Horatio Caine.
Catherine and Nick become absorbed in the dangerous world of street racing after the body of one of the illegal sport's drivers is found in the desert at an abandoned airstrip. Grissom and his crew probe the sudden death of a renowned poker player who had a violent convulsion during a high-stakes game.
A wild night in Las Vegas has the CSIs simultaneously investigating four fatalities. Greg Sanders' first day in the field has him assisting Grissom's investigation of a fatal nightclub shooting. Meanwhile, Catherine probes into the death of a stripper found dead in a hotel room, while Sara and Nick look into the strange case of an "alien" body found near Area 51.
Grissom and Sara investigate the murder of a woman after a swap party. The married couples in the neighborhood meet and switch partners. With the help of a crime scene cleaner, Nick and Warrick find there was more to their crime scene than they first thought. Catherine wants a promotion to day shift supervisor.
Catherine, Warrick and Nick find the body of two women at a construction site buried under tar.The swing swift are brought into the world of foreign "mail-order" brides. Sara and Catherine have a dispute in which Sara gets suspended by Ecklie for acting insubordinate toward Catherine and himself. Sara opens up to Grissom about her childhood past.
Two amorous freshmen are found dead on a sleeping bag in a dorm room, and Sara and Greg run into one dead end after another as they try to determine why the students were killed. Warrick, Nick and Catherine figure out how a man is found dead in the center of a crop circle. Ecklie is called into duty for a man found dead in his car and his body later goes missing.
The two forensic teams come back together under the leadership of Grissom and Catherine just in time to tackle three separate investigations: a murdered couple found in bed in a suspicious trailer explosion; a beautiful stripper discovered dead and dumped in the worst part of town; and two bodies found baked and decomposed after spending five days in the trunk of a car exposed to the hot Vegas sun.
Catherine and Brass investigate the case in which a man is found dead in a dumpster. It soon turns out the man had a serious food problem. The trail of his death soon leads to a hotdog-eating contest.Meanwhile, Nick and Sara investigate a not-so-amicable divorce with a bizarre twist. So bizarre it eventually lead to murder when both are found dead and it looks like the dog killed one of them.
The CSI's are called out to investigate the disappearance of a boy whose father died four years ago. Soon a couple is arrested at a convenience store with a boy matching the description of the missing kid. The only problem is they both claim it is their son. Both parents have exactly the same picture of the boy, with a scar on exactly the same place on his face. They hope a DNA-test could confirm who the real parents are, but when this information comes to light, it lead to another bizarre twist, possibly murder.
The CSI team investigates the murder of a man suffering from a congenital hypertrichosis, causing him to grow excessive body hair. Elements of the case suggest a connection with a belief in werewolves. The case leads to the victim's sister, who suffers from the same disease. Because of her condition, she'd been hiding from the world, but it turns out that she's hiding facts that are vital to solving the case.
A man accused of murdering his wife and co-workers leads the CSIs on a wild ride through a busy casino, eventually barricading himself and a hostage in a casino hotel room. The CSIs process the evidence from the crime scene to determine whether or not the man acted alone or had an accomplice. One of the CSIs eventually steps in as a hostage negotiator, putting himself in danger.
In part one of this two-part seventh season opener Grissom and Catherine handle the case of a women's dead body found at Cirque du Soleil by a performer. An investor at one of Sam Braun's new casinos is shot to death during a party on the rooftop. Catherine's life is in jeopardy after visiting a nightclub with Nick. Grissom finds a miniature replica of a crime scene that he is investigating.
Coming straight from the perspectives of five people: Donna, Rebecca, Jack, Lou and Ray. All with one thing in common. They’re all dead. Brass and Catherine get to handle the case of Donna, who’s a cop from San Francisco, moonlighting as a bodyguard. Warrick and Greg work the case of Rebecca. Nick and Sofia handle the case of Jack, a returning veteran from Iraq. Grissom and Sara take the case of Lou and Ray whose bodies were found in Lou’s garage.
Grissom investigates when a worker at a poultry processing plant is found dead in a stun bath used to electrocute chickens before they are slaughtered. Nearby, a miniature replica of the crime scene is discovered. It's eerily similar to two other replicas left at scenes of homicides. Also, a man and a dead woman are found stuck in cement at a construction site; and an elderly Russian woman is discovered dead in her apartment with her head in a gas stove, but Warrick thinks she was murdered.
Catherine testifies in a murder trial in which a man is accused of murdering his own mother three years ago, but the suspect is found not guilty. Catherine, however, believes he did commit the crime and that he may also have killed two other people, so she sets out to find the other victims. Grissom prepares to leave on a four-week sabbatical.
Once he unseals a package sent to him through the mail, Grissom is floored when he finds a miniature crime scene inside. The finding is entirely more perplexing since the successive killer accountable for earlier related miniature crimes is now deceased. Grissom plows to examine the miniature and discover the actual location, when the investigation makes it clear the murder showed has yet to happen, but is probably going to happen soon.
Grissom and his team are discouraged when they find a pool of blood as they begin investigating the disappearance of a high school basketball star and his cheerleader girlfriend. Grissom's quip that the young lovers may have run off to Mexico is soon quashed by the discovery of drops of blood by Ryan's vacant parking spot at the school. After finding a letterman jacket and cheerleading sweater in the field house and a pool of Ryan's blood nearby, the team tries to determine what went awry.
As the CSI's continue their search for and discover the identity of the "Miniature Killer", Grissom and Sara's relationship gets exposed to the rest of the team as she goes missing during the investigation. The 'Miniature Killer' is finally captured, but not before a member of CSI becomes the killer's final victim.
The sky is falling or at least people are. The CSI's try to figure out if it was murder or sucide after a man is dead after falling from a hotel. Across town, a elderly woman falls through her table and her husband dead in the shower. The only two witnesses to the crime are an incooperative cat and a parrot who pleads the fifth.
Jason McCann contacts Nick and says that he's in imminent danger. Langston has a courtroom war of nerves against serial killer Nate Haskell. A bomb tech disarms a bomb attached to Nick's house. But when he accompanies Nick, Catherine and Vartann to a warehouse with multiple booby-traps per square inch, Kip has to really earn his paycheck to find a safe way out for the CSI team.
All hell is breaking loose in the aftermath of the shooting of Eckley, the kidnapping of Russell's granddaughter, and Stokes quitting. Fin seems to have disappeared, causing the CSIs to be short-handed and struggling to keep up. Given the personal nature of the case, Russell becomes heavy-handed and reckless in his effort to dig up fresh leads.
The season 5 finale was directed by Quentin Tarantino. In this featurette, the CSI cast and crew recount Tarantino's work while the director discusses the episode.