A child is abducted. As the Amber Alert goes out, the entire team investigates in a race against time. Lindsay Willows is found hitchiking to the alarm of Catherine.

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 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. Sophia 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 kiddnapping 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. This development 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.

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 Nick 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. A boy confesses to the killing of his brother, but evidence suggests that he may not have committed the crime.

Grissom, Sara, and Nick 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.

A man (Alan Rosenberg) whom Catherine flirted with at a bar reappears in her life as a suspect in a murder investigation.

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 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 five feet of dirt.