Some provocative episodes from Season 5 of CSI involve Russian mail order brides ("Nesting Dolls"), infantism ("King Baby"), and the Mexican lifestyle of narcocorrido ("Snakes"). From the creative storytelling ("4x4") to the macabre ("Who Shot Sherlock?"), there's something in Season 5 for everyone. The CSI team investigates many crimes that hit close to home as well. Grissom comes under fire from Ecklie ("Mea Culpa"), Brass tracks down his estranged daughter ("Hollywood Brass"), and during the course of the season Greg Sanders completes his transition from the lab to the field.
A feverish night in Las Vegas results in one dead male in an alien suit, one more dead male in a bathtub, one dead female with two suspicous men at the scene, and another dead male with a polaroid of yet another dead male, but on the other hand, we get to meet Greg´s replacement DNA person.
Heavy rains in Vegas wash up a body in the storm drains. As the team investigates, they find bones in the sewer system that could only be murder. The body was dumped in the sewer opposite a house that turns out to be filled with high explosives. Also, Greg attends his very first autopsy but keeps it all in.
A young girl is abducted from outside a convenience store, triggering an Amber alert. The team investigates in a race against time. The girl's body is soon found and the team discovers that she's been dead for longer than they thought. Also, Lindsey Willows is found hitchiking to the alarm of Catherine, and Greg has another replacement.
A woman is found dead in a hotel suite with symptoms of the ebola virus. However the dead woman and another woman found later have similar symptoms, are linked to a health spa selling cures to help slow the effects of aging. Catherine and Nick investigate. Sara and Greg with help from Grissom try to determine how the owner of a home was killed while his home was tented for infestation. Both of his neighbours inhaled the poison used during the fumigation.
Grissom and Sara investigate the murder of a woman after a swap party where the married couples in the neighborhood meet and switch partners. Nick & Warrick investigate the murder of a landlord killed by a band saw. With the help of a crime scene cleaner, they find there was more to their crime scene than they first thought. Ecklie is promoted and Catherine wants a promotion to day shift supervisor.
The killer from The Execution of Catherine Willows returns with deadly results. The entire team is engaged in a race against time to stop this sadistic killer from succeeding again. Grissom is additionally distraught by the idea that this killer is smarter than he is.
Grissom is called to a murder of a 17-year-old in a casino penthouse. Sofia Curtis (Louise Lombard) joins him in his research, she normally works in the day-shift. The entire team gets involved when its discovered that a kidnapping took place along with the murder.
A woman who was pulled over by police is found murdered two miles up the road from the stop. It's not long before Robbins determines that the woman is, genetically speaking, not a woman.
Grissom is confronted with new evidence while on the stand of a murder trial of a restaurant owner. Warrick investigates the death of a John Doe killed by a modified semi automatic weapon, which goes off accidentally in the lab. The new evidence in the murder trial requires the reopening of the case and Eckley initiates an inquiry into Grissom and his team. The results of the inquiry lead to dramatic changes of the CSI team and the series.
Grissom and his team investigate the starving death of a five year old boy. They discover the boy has siblings who are in danger too. Catherine and her team determine who killed a prisoner in a holding cell brawl.
Greg, for his final proficiency, has to determine how the Sherlock Holmes of a Sherlock Holmes club was killed. Nick and Warrick try to determine how the driver of jeep was killed when the car ran off the road. They have to do this under budget while Catherine is watched by Ecklie.
The swing shift has a busy time. Warrick looks into the murder of man by someone who apparently needs a wheelchair. Nick looks into the murder of woman in the subculture of the narcocorrido, songs about drug murders. The night shift is slow and lends help to Catherine's team.
Catherine, Warrick and Nick find the body of two women at a construction site buried under tar.The swing shift are brought into the world of foreign "mail-order" brides. Sara and Catherine have a disputer in which Sara gets suspended by Ecklie for acting insubordinate toward Catherine and himself. Sara opens up to Grissom about her childhood past.
Grissom, Sofia, Sara and Greg investigate the disappearance of a woman coming home from a night out with a friend after her abandoned car is found on the edge of a highway. Catherine, Warrick and Nick investigate the deaths of a hunter and his prey, a Kodiak bear. Also, Sofia wants to leave the lab - she's unhappy about no longer being a supervisor.
When a major Las Vegas player is found dead, Ecklie orders both teams to investigate the case. The man who had secrets on everyone in Vegas had a very big one of his own.
Catherine, Nick, and Warrick investigate a badly mutilated body in the woods. The cause of death was a shotgun blast. Nearby is a beaver dam made in part with cash. Grissom, Sarah, and Greg try to determine how a man was killed in a hotel room. It leads them to a convention of big women.
A serial killer strikes again, and the CSI team tries new technology using evidence from a prior killing. They find a fingerprint belonging to Jesse Acheson, who becomes the prime suspect. Nick and Catherine investigate the murder of a young boy found dead in his bed. His brother confesses to the killing, but evidence suggests that he may not have committed the crime.
Grissom, Sara, and Greg investigate a wildfire that killed one man and badly burned a woman. Catherine, Nick, and Warrick get the case of a family of three murdered in their home.
One night, four cases. Grissom and Brass get a stolen hummer and a taco stand. Warrick gets a dead car show girl. Sara and Greg get a dead bodybuilder. Nick gets a dead boy found on a bench.
Brass travels to Hollywood, California to try to track down his estranged daughter's friend, meanwhile trying to rekindle some kind of relationship with her.
Grissom and Sara investigate the murder of a mental-hospital patient and quickly narrow down the suspects to a handful of other patients and staff members.
A man (Alan Rosenberg) whom Catherine flirted with at a bar reappears in her life as a suspect in a murder investigation of a woman who was shot and killed.
Two amorous freshmen are found dead in 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 CSI teams come together to save one of their own when they learn one team member has been kidnapped and buried alive, and now they must find him before he suffocates under 5 feet of dirt.
After Grissom gives the kidnapper the ransom money, the kidnapper blows himself up. The team must band together and cover every piece of area to find Nick. The team gets close, but then run into a couple dead ends. The clock is ticking and time is running out for Nick who is suffering and suffocating underground.