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.

Grissom, Nick, and Sara search for a kidnapped woman and find more than they expected. Catherine and Warrick investigate the hit and run death of a little girl.

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 under a house buried in cement.

Royce Harmon was murdered 3 months ago in a scene staged to look like a suicide. Now another murder has taken place. Whoever the killer is he has a thorough knowledge of forensics, he purposefully has left evidence, and has baffled Grissom and his team. Warrick and Nick investigate the case of a man who went over a cliff in his car and is now unconscious.

A man convicted of arson and the murder of his wife and child seeks assistance from Grissom to help prove his innocence. Meanwhile, Catherine and Nick investigate the underground world of sports gambling when a teenager is murdered at close range.

At a swanky fundraiser, attended by the sheriff, a woman turns up dead in the pool. The owner of the house is away and a young couple is housesitting. Warrick looks into an apparent professional hit in the glass elevator of one of the hotels.

The entire team investigate the abduction of the infant child of a well to do family. Suspicion immediately falls on the child's parents.

The team is investigating the ongoing murders by a signature killer. The killer has some knowledge of forensics and has left little evidence behind. With the investigation somewhat stalled, the sheriff invites the FBI to join the case. This makes Grissom angry and it only gets worse when Sara offers to bait the killer.

Grissom and crew are called in after high roller Tony Braun, a known drug addict, is found dead in his house by a gardener. Since drug paraphernalia is discovered near his body and it is also determined that he had recently inhaled heroin, the cause of death is at first thought to be an overdose. But further examination of the corpse reveals that Braun had been restrained at some point with duct tape, leading Grissom to believe that the victim was forced to ingest lethal amounts of heroin and, perhaps, other drugs.

Grissom and his team investigate a murder suspect who is caught red-handed -- burying the victims -- while Catherine and Warrick take on the case of a woman found dead in a hotel spa.

Grissom, Catherine and Sara are called in to investigate the death of a hockey player on the ice. Warrick and Nick look into the apparent drug-related death of a sax player at a casino.

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 one of the illegal sport's hotshot drivers is found dead out in the desert at an abandoned airstrip. Back in town, Grissom and his crew probe the sudden death of a renowned poker player who suffered a violent convulsion in the middle of a high-stakes game with three others. It looks like natural causes, at first, but Grissom suspects foul play.

Grissom investigates when a woman vanishes while taking part in a magician's act. The female volunteer is placed inside the Amazing Zephyr's "Chamber of Doom" and the illusionist thrusts swords through the box. When it's opened, she's gone---and doesn't reappear in her seat as she's supposed to. Only traces of blood are left inside the chamber. Clues lead the CSIs to an eerie, decrepit mansion filled with secrets. Elsewhere, a rock star's death on a band bus appears to be the result of an overdose, but Catherine uncovers evidence that points to murder.

Warrick investigates the drive by murder of a young girl in his old neighborhood. The girl's father is a friend and mentor of Warrick's as well. Warrick struggles to control his emotions to the point where Grissom pulls him off of the case. Nick tackles the murder of a computer company employee. The only supects are the three other employees in the building.

Things get personal for the CSIs in the top-rated series' third-season finale, which explores the intersection of the investigators' work and their personal lives. Three masked bandits steal a safe-deposit box from a Las Vegas bank in a daring daytime heist, during which Det. Lockwood is killed. Lockwood's death provides Grissom and his crew with added incentive to find the murderous culprits. But the case really hits home for Catherine when the evidence leads to casino owner Sam Braun, who is like a father to her. Also, Grissom's hearing gets progressively worse and he seeks out Dr. Robbins for help.

A severed head is shipped to Dr. Robbins from Jackpot, Nevada. Grissom goes to Jackpot to find the rest of the body and gets very little cooperation from the locals. Catherine gets an unexpected gift from her father.

Warrick's appearance at the preliminary hearing on a rape and murder case goes terribly wrong when the only piece of evidence is thrown out on a technicality. Grissom and the team have 24 hours to make the case with new evidence or the killer will go free.

Three little CSIs (Grissom, Sara, and Nick)respond to an electrocution at a casino. The casino is hosting Japanese antiquities. The electroctution is just a ruse to steal the central piece of the exhibit. Catherine and Warrick deal with a vampire murder.

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.

The CSIs come across an abandoned military compound being used by a small cult. The CSIs grow suspicious when they see that a mass suicide has taken place, but only 11 of the 12 beds are occupied.

The team must investigate the death of a police officer who died during a shootout leaving hundreds of bullets on the crime scene. The case becomes complicated when it turns out that Sofia Curtis and Jim Brass were with the victims during the shootout. When it turns out the officer died from friendly fire, it is up to the team to find out who fired the fatal shot. Meanwhile, Sofia is wondering whether she fired the fatal shot or not. She decides to hide the fact that the officer stepped into her line of fire, afraid it will ruin her career.

The CSIs crash an elegant party for the city's crème of the crème to discover who killed a young man. The case gets a bit more personal for Catherine when her father, Sam Braun, is one of the suspects.

Grissom and the team join forces with Jack Malone, an FBI Agent from New York to track a serial killer.

The crossover continues on Without A Trace S06E06 Where & Why (II).