CSI: Crime Scene Investigation follows a team of crime scene investigators (CSI's for short) employed by the Las Vegas Police Department (LVPD for short) as they use physical evidence to solve murders.
The team is originally led by Dr. Gil Grissom (William Petersen), a socially awkward forensic entomologist and career criminalist who is promoted to CSI supervisor following the death of a trainee investigator. Grissom's second-in-command, Catherine Willows (Marg Helgenberger), is a single mother with a cop's instinct. Born and raised in Las Vegas, Catherine was a stripper before being recruited into law enforcement and trained as a blood-spatter specialist.
Following Grissom's departure during the ninth season of the series, Catherine is promoted to supervisor. After overseeing the training of new investigator Raymond Langston (Lawrence Fishburne), Willows is replaced by D.B. Russell (Ted Danson) and recruited to the FBI shortly thereafter. Russell is a family man, a keen forensic botanist, and a veteran of the Seattle Crime Lab.
In the series' twelfth season, Russell is reunited with his former partner Julie Finlay (Elisabeth Shue), who, like Catherine, is a blood-spatter expert with an extensive knowledge of criminal psychology. With the rest of the team, they work to tackle Las Vegas's growing crime rate and are on the job 24/7, scouring the scene, collecting the evidence, and finding the missing pieces that help solve the mystery.