Several couples are killed bloodily after a wild party night in the same luxury hotel with Cameron and Mandy Klinefeld, or rather one somehow forced to kill the spouse. Nick is pleased to bump into former college mate Kenny Richmond, who works there, until it seems buddy boy passed confidential information to the press, which could get Nick fired.

A grossly decomposed corpse in a bath tub is identified as frat student Daniel O'Hannissey. He was last seen in a bar, taking part in a brawl about team sports, but left apparently unhurt. Meanwhile, the serial couples killings investigation takes a sharp turn when both are murdered in their home, while the undercover police observation was diverted.

Fingerprints suggest a link between two home invasions, but it's hard to link either the victims or the logical suspects, who may all be innocent. The crucial survivor testimony proves the most tenacious problem. A toddler found and accidentally fired a murder weapon in the family's suburb garden. Its place is a mystery, being so overt and unrelated to the victim, a bounty-hunting has-been, until the team consults the sky.

During a week-log heat wave, corpses are found, mostly accidentally. A.D.A. Jeffrey Sinclair decides to 'make an example' of a workaholic father who forgot his baby-boy in his scorching-hot car with fatal result, but the team finds the couple lost a previous baby and may have murdered this one. Mark Young is missing since his teen date's fatal lake sports accident. A fat man on a crazy diet was electrocuted at home.

The discovery of a dead man in the wilderness in a fursuit leads to an investigation at the goings-on at a furry convention.

The sheriff of desolate town Jackpot calls in CSI for assistance after a severed head is found. The sheriff proves rather more cynical than helpful towards Grissom, unlike the veterinarian-coroner. The rest of the corpse is found buried to the shoulders alive, a Native American torture technique. Grissom triumphs over sabotage and works out the local reports and relevant secrets.

Because Warrick naively assumed simple uniformed cop Hal Watson would have arranged a search warrant, the crucial weapon in the rape and murder trial on a neighbor against Michael Fife is dismissed as evidence in court. A.D.A. Jeffrey Sinclair can only get a 24 hours delay to present new evidence to build the case again. Nick brilliantly smooths emotional waywardness from Sarah and Warrick. New clues expected to reconstruct the case against Fife actually indicate he's probably innocent. An alternative culprit must be found, starting from Fife's car where the bloody knife was planted.

Julie Waters, a dancer, has been missing for 6 days. A suspect, Howard Delhomme, calls the police and turns himself in. He refuses to talk to anyone but Catherine. Sarah and Nick want to work on this case because they see it as a career-making step. Grissom, to their anger and disappointment, hands the rein over to Catherine. Despite their initial antagonism, they all worked together to find the young girl.

Sheriff Rory Atwater is leaving the Orpheus hotel and witness a car bombing, where the driver, the valet and the bellhop die. Grissom and Catherine arrive to investigate the crime scene and gunshots start. Grissom finds that the bullets are in the trunk in bag. Nick and Capt. Brass help the investigation. Soon they learn that the driver is Air Marshall Adam Watson, and the car was rented in an agency. Nick puts together the pieces of the bomb, which was a pipe bomb connected to the car clock. Soon they conclude that the victim might have been the previous user of the rented car since the timer was not accurate. Meanwhile, Sara, Warrick and Det. Louis Vartann investigate the death of Amelia Reuben, who is the wife of the successful singer Myles Reuben. They conclude that Myles, his manager Sam Hopkins and a hotel waiter were the last persons to see Amelia alive, and the autopsy and Greg's investigation concluded that she was poisoned.

Teenager Brian Haddick is found on a construction site, skull fatally smashed, with an employee's hammer. Grissom's team checks on the construction crew as well as Brian's school crowd, stumbling on abused love and dirty practices. Another victim was killed by a bullet which literally fell from the sky.

A juror dies during a trial in a heavily guarded safe house. A four-year-old case of a missing woman is reopened when the woman's sister gives the CSIs new evidence she withheld during the original investigation.

When the nurse Debbie Marlin is found murdered in her bathroom, the CSI team investigates the case. They learn that Debbie was a promiscuous woman that used to date doctor. Her last boyfriend Dr. Michael Clark is missing and becomes the prime suspect of murdering her. However, their further investigation finds pieces of his body in plastic bags in several trash bins in an alley. Dr. Robbins concludes that the cuts have been made by a surgeon using probably a scalpel.

In the Mediterranean Casino, Ty Caulfield is speaking for guests that the casino will exhibit rare Japanese antiques from the Seventeenth Century owned by Mr. Yuri Yamamoto in the casino. Out of the blue, a woman cries and they see a body floating in the pool and a live wire at the edge. Grissom, Sara and Capt. Brass investigate the case and soon they find that the body is a CPR dummy. They hear the security alarm and find the guard wrapped up in duct tape, and the samurai sword is missing. They investigate the findings and return to the exhibition room to collect other evidences but the room is empty. The head of the casino security tells that the pieces have been transported to the casino vault to be in a secure place. Soon Grissom finds the sword hidden in an air duct and questions Yamamoto why a Nineteenth Century armor was together with the other pieces Surprisingly Yamamoto say that he has no armor in his collection. They go to the vault with Ty and find that all the casino money has been stolen, in a masterstroke. But their findings do not stop. Meanwhile, Catherine and Warrick go to an abandoned house with fame of haunted and find the corpse of Angela Sommerville with two holes in her jugular vein and drained without any blood. Further, there is no gore in the crime scene. Soon they learn that Angela used acrylic fangs and her friends belonged to a vampire "coven".

There is a heist in a supermarket with five casualties, including police officer Clay. The entire CSI team investigates the case. Officer Fromansky, Grissom's longtime foe and who killed the robbers and a civilian, claims that there was a third robber on the scene. However, the evidences do not corroborate with his testimony. The CSI proceed the investigation and conclude also that it was an inside job. Will they find the truth?

Although living in a well-protected gated community, the couple Mike and Laurel Trent are executed in front of their house by two masked killers. They were owners of the famous Acid Drop club among other properties. Grissom notes that Laurel was dragged out of the car, but Mike was dragged down the driveway in a place where everyone could see him. The whole team is assigned to investigate the case since the real state is large. Soon they find that the jewels have been robbed and Laurel had made porn films in the past with the production of Drake the Snake. Catherine goes to the Acid Drop and interviews the manager Chris Bezich first and Drake, who is bartender, later. Their further investigation shows that Mike's former partner Kyle Goode is suing him in the justice. When Grissom is summed to a murder case in an apartment, he finds evidences that will help him to resolve the case.

A man who works at a half-way house is found dead in an area filled with drug addicts and prostitutes at night. His belongings were stolen, from car to shoes. Another body is found wearing only his boxers, with signs of a clown's make-up.

While trying to pass a bus on the highway, an arm strikes the windshield of the car of a couple. Catherine, Nick, Sara and Capt. Brass investigate the crime scene and find pieces of a woman secured by white strips of clothes on the bottom of the bus that was carrying inmates from a prison to a church. They believe the woman was trying to flee from the correctional facility. Soon they learn that the victim is Antoinette "Baby Girl" Stella that would be released on the next month. Sara and Nick go to the prison to try to understand why Baby Girl decided to escape. Meanwhile, Grissom and Warrick investigate the murder of Adanto Adams who was stabbed to death at the home of his intellectually disabled brother Zero. Soon they meet Zero and his guardian Frank Samuels and they learn that Adanto has promised to his beloved brother Zero that they would be rich. Warrick gets the videotape of the casino where Adanto went to play blackjack and lost a fortune.

A strong and tall man follows another man in the casino to the parking lot. Soon the CSI team comes to the casino to investigate the murder of the man, Tony Sciarra, who was brutally beaten. They watch the tape of the surveillance cameras and see a shorter man stealing Tony's chips and being followed by him. When they identify the killer, Walter Darian, they arrest him; however, the guy attacks Grissom first in the interrogation room and then the guards that try to subdue him. Out of the blue, Walter is dead. Now, they investigate his belongings since he was an accumulator and find evidence that may lead them to another murder case.

There is a fire in a house and Catherine, Nick, Warrick arrive at the scene. An arson investigator tells them that there was a fire in the block ten days ago, maybe caused by a serial arsonist. The Abernathy family is rescued, but the daughter Sabrina that was not supposed to be at home is found dead. They begin their investigation looking for the origin of the fire and for suspects. Meanwhile, Grissom, Sara and Capt. Brass investigate the death of a man found dead in a hotel bathroom. In the autopsy, Dr. Robins finds a round tile with the letter in his throat, and five more tiles in his stomach. Brass identifies the victim and Adam Brenner from Florida that was in Las Vegas to participate in a logo game tournament. Soon Grissom learns that Adam was a top player and Grissom looks for opponents defeated by Adams that might be angry.

During the police marathon in Las Vegas, Grissom sees a runner outside the road and drives his car to the place, leaving Catherine alone. He finds a police officer dead. Dr. Robbins find that the victim was in excellent shape, but he had ingested two substances that combined killed him. Meanwhile, Sara, Warrick and Det. Louis Vartann investigate the murder of officers Manny Senteno and Patricia Fielding in a hotel room. Warrick's first impression is that might be a murder-suicide case. Soon they find fingerprints of the police officer Lydia Lopez and learn that she was lodged in the next-door room. When they look inside the room, it is completely trashed. Lydia says that she had sex with a Manny once a year during the marathon and she believes that her husband Archie Lopez might have followed her and trashed her room, but would never kill Manny and Patricia.

When a roller coaster derails in an amusement park, there are six victims in the parking lot. Grissom, Nick, Sara and Capt. Brass investigate the case and soon they find that five deceased persons were in the train, but the employee Jim Nevins died twenty-hours before with a head trauma. Grissom interviews the park chief engineer Woody and learns that the old roller coaster has good maintenance. Grissom shows a nut to Woody and he says that it would be impossible to cause the train derail since there are eight sets that would have to lose. Meanwhile, Catherine and Warrick investigate the murder of the thirteen-year-old Tessa Press that was found murdered but not raped. Her mother Raina tells them that Tessa used to go to the house of a friend twice a week and she had assumed that her daughter was with her friend. Now they need to find what has happened to her.

The body of a young gambler is left at a neon graveyard. He died from two gunshots to the back of his head. Prior to his death, he won a lot of money from one of Sam Braun's casinos. This makes Grissom remove Catherine from the case.

When Linley Parker survives a rape attack, the CSI team investigates the case. Linley identify her aggressor Dr. Todd Coombs, but their DNA do not match and Todd is released despite the identification. His brothers become the suspects based on the DNA results, but they do not find the guilty. When Linley is murdered, the CSI team discovers new genetic condition in the case.