A 28 year-old single mother is found dead. Initially, it's believed to be a suicide, but Catherine determines she was murdered. Also, Ecklie summons Grissom to refute the testimony of an entomologist in a murder trial.

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 sift through the overwhelming evidence from a shootout with drug dealers in order to determine who is responsible for the death of a police officer killed during the incident.

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.

A wealthy defense attorney is killed at her son’s wedding but Nick’s car, containing all the collected evidence is stolen and the case is compromised. After discovering new evidence, the team suspects that someone from the wedding party may be responsible for the murder.

In the season finale, the CSIs wait by the bedside of one of their own when he's shot in the line of duty. One CSI faces a hard choice by having the power of attorney over their injured friend and colleague. Meanwhile, the team also investigates the strange way of life of one man when he is found decapitated by a train.

At Keppler's request Catherine uses a different approach to catch the killer, and in doing so she deceives the rest of the CSI team. The team soon discovers that something is amiss in Catherine’s investigation.

After a man is killed in his limousine, Greg finds that the murder victim has ties to the man he had to kill in self-defense. The team finds that the brother is involved in this investigation and has to deal with him and his hostile mother.

The team investigates an underground mob. Warrick ends up becoming the prime suspect in a murder that's related to the mob, and his addiction to pills starts to have a significant impact on his job as a CSI.

Catherine comforts Warrick when he is accused of murdering a famous Vegas gangster and even he is uncertain of his guilt or innocence.

After Warrick is shot in a Las Vegas alley, the CSI team comes together to deal with the aftermath.

Season finale: The investigation of a triple homicide leads to the discovery of corruption running rampant throughout the LVPD. The closer they get to the truth, the more serious are the repercussions. To be continued...

D.B. Russell leads the CSI team on a hunt to find his kidnapped granddaughter.