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 are 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.
The entire CSI team investigates a disappearance at a local university. A young woman vanished, seemingly off the face of the earth. Forensics leads them to possible suspects, and possible suspects all have probable motives, but nothing seems to pan out. This leads our team to discuss the "Chaos Theory." When combined, many seemingly-innocuous events may have a deadly outcome. And closure is not always within reach.
Grissom investigates a possible suicide at a high-profile construction site. Against the wishes of the Sheriff, Grissom pushes to get at the truth of the matter-he thinks the suicide was actually a homicide, and uses theories on electrocution to look for his killer. Meanwhile, Nick and Catherine take on a case with little more than angora fibers to follow. A teenage boy dies while in session with his female psychologist, and traces of angora on his underwear make them believe the psychologist may be practicing very unconventional methods of "therapy."
When the class clown at the local high school is found murdered, the CSI team is called to investigate the student, who is also the top jock on campus, is found shot in the back in the school bathroom. The CSI team quickly discovers that the victim was also the class bully, and Grissom is convinced that he is looking for a classmate who was finally pushed to end the abuse once and for all. The team uses sophisticated new equipment to track the scent the killer left behind. Meanwhile, Sara and Nick investigate a case involving a severely decomposed body of an Army veteran found in a bag.
Grissom, Sara and Warrick are called in to investigate an abandoned, blood-splattered apartment and Nick and Catherine must examine a dead scuba diver lodged in a tree. The team members are suspicious when the former tenant of the bloody apartment claims that his missing girlfriend is visiting her parents -- and the parents say she never showed up. Meanwhile, Nick and Catherine are called to the site of a large fire and are confronted with the scuba diver found dead in the top of a tree near Lake Mead. Is it a murder or an urban legend turned fact?
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. As Grissom, Nick and Sara investigate the seemingly clear-cut murder case, Grissom questions the simplicity of the evidence when he discovers that the suspect burying the victims is the brother of a convicted felon. Meanwhile, Catherine and Warrick must determine if the woman found dead in the hotel spa was the victim of negligence, foul play or heat-induced natural causes.
Grissom and Nick investigate the death of a book restorer while Catherine and Sara are called to the scene of a fatal train crash. When the female book restorer is found dead and locked inside a "cage," a temperature-controlled workspace, Grissom and Nick attempt to determine whether this is a case of suicide or homicide. They discover that the key to solving the case may be a co-worker who suffers from autism. Meanwhile, Catherine and Sara are sent to comb through the wreckage of a collision between a train and an SUV and find out if it is a case of road rage or simply an accident.
Grissom and Catherine investigate the apparent violent death of a woman found in a sandbox. Their investigation leads them to the underground world of s and m clubs. Meanwhile, Warrick and Sara are called to a crime scene to investigate a shooting, which initially appears to have taken place during a robbery.
Grissom and his team investigate a casino heist during which innocent victims were shot, while Catherine and Sara are called to the scene of a murder in a remote part of the desert. The evidence found at both crime scenes -- the crowded local casino and the isolated desert convenience store where a clerk was murdered -- has the CSI team drawing a correlation between the two crimes.
With Grissom away, Warrick is in charge for the first time as the team investigates the murder of the con artist, who has run off with some tourists' money only to get shot and killed in the parking lot. The prime suspect in the case turns out to be Captain Brass' daughter, which causes Brass to take himself off the investigation professionally, but not personally.
The CSI team is called in when a famous real estate entrepreneur is found dead in a hotel elevator. When the body of Bob Fairmont, the real estate developer, is found, the team discovers that the crime scene has been tampered with and that the victim has been re-dressed. After tracing the cause of death to a lethal poison, the team is shocked to discover that Fairmont's organs have already been removed and donated, making the case a bit more difficult to solve.
Grissom and Sara are called to the crime scene when two murder victims are found hidden in pipes at a construction site in the middle of an alfalfa field, while Catherine and Nick investigate an ostensible hunting accident. The investigation of the construction site murder reveals that the victims were sisters and the relationship of one of the sisters to a former prison inmate is a cause for suspicion -- especially when his presence is traced to the scene of the crime. Meanwhile, Catherine and Nick begin to doubt seriously that the body found in the woods was the victim of a hunting accident.
Grissom's nemesis, serial killer Paul Millander (Matt O'Toole), 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, which Millander witnessed as a boy. In each case, the victim is shot once through the chest while lying in a bathtub. A nearby tape recorder contains the person's supposed suicide message. All three victims share the same birthday of Aug. 17---the date Millander's father was slain---with the years in descending order from 1959. So presumably, the killer's next target was born Aug. 17, 1956...which just happens to be Grissom's birthday.
Catherine is ordered by a kidnapper to accompany a man who is to deliver $1 million in ransom to him or else he will kill the man's mistress. But when the million is paid, they learn that his mistress is already dead.
Grissom investigates the murder of a Las Vegas photographer whose remains were dumped at a nearby body farm where CSIs routinely study corpses, and his findings reveal that the man was apparently shot to death even though there are no bullet fragments in the body. Also, Grissom's leadership is questioned by some members of his staff.
When Terry Rivers barrels into the opposing team's goalie, a fight breaks out and Terry ends up at the bottom of a huge pile of bodies. After the players are separated, he is found dead...with a deep, bloody gash across his neck. Grissom, Catherine and Sara are called in to investigate. Across town, Warrick and Nick look into the apparent drug-related death of a sax player at a casino. While working on the case, Warrick finds himself drawn to a rising young singer who worked with the dead musician.
Grissom investigates the murders of four monks who were shot point blank while chanting in a Buddhist temple; Catherine reopens a cold case in which her best friend was murdered, after the man convicted of the crime claims he's innocent shortly before he dies.
A bus carrying 23 passengers from Los Angeles to Las Vegas crashes less than 40 miles from its destination, killing nine people. Before he dies, the driver recalls that, moments before the wreck, the steering wheel began vibrating like a jackhammer in his hands, making it impossible for him to control the speeding vehicle. When the bus finally did come to a stop, it was on its right side on top of a sports car that was following it. At the scene, the CSIs discover that a recent parolee was on the bus, but is now unaccounted for---and that there's evidence of foul play.
Jane Galloway is a nervous breakdown waiting to happen. She has completely shielded herself from the outside world, but that doesn't stop a stalker in her attic from killing her. When CSI arrives, they find her hair dyed and her face shoved in the toilet. This image has a heavy impact on Nick, and they soon realize that this stalker is well acquainted with Nick, which makes the CSI the next target.
Grissom and Catherine investigate the stabbing death of an 80-year-old woman who lived in a run-down house full of cats; Nick and Sara comb through the remains of a car bombing that was, apparently, a murder plot gone awry.
Grissom and Sara investigate when a man's body, which has been doused with lye, is found buried in a park; Nick tries to determine how a hiker apparently drowned in a desert.
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. When several motorists report seeing the girl along an access road near Miami, Catherine and Warrick fly there and meet that city's top CSI, Horatio Caine, who aids them in the investigation.
Season Finale. The CSIs investigate when the body of an unidentified young woman is discovered stuffed in an overturned shopping cart near a freeway underpass. Her horribly disfigured and partially decomposed face is a nightmare of blood, scabs and scars, as if she'd been shoved into a fan. A huge circular hole dominates her left cheek. Someone not only wanted her dead, Grissom reasons, but "they wanted her ugly." Adding to the mystery are the cart's other contents: an expensive handbag, fashion magazines and a leather day planner with notes written in code.
