Catherine Willows, until 2012, was a CSI Level Three and the Graveyard Shift Supervisor with the Las Vegas Police Department.
Raised in Vegas by a showgirl mother, Catherine became an exotic dancer and nightclub wild child. Finally finding her calling, she danced her way through a medical technology degree at UNLV, hung up her spangles and became a CSI, specializing in blood spatter analysis. Her supervisor, Gil Grissom, mentions the fact that she was his first friend in Las Vegas, and the first person he recruited for his team. While a reliable and meticulous CSI, Catherine still enjoys flaunting her sexuality, and occasionally uses it to make a point - or win over a difficult suspect.
Catherine is a single mother with an attitude and a complicated family life. Her late husband Eddie, from whom she "should have gotten divorced years ago" had issues with drugs and fidelity, and was murdered in 2003. Their teenaged daughter Lindsey seems to have acquired her mother's feistiness - talking back, running away, and hanging out with questionable friends. Catherine, despite her night-shift schedule, keeps a close watch on her, placing her in an highly disciplined private school, and spending as much time as possible with her during the day. Lindsey is soon to graduate and go to college, a fact that causes Catherine no end of anxiety.
Casino tycoon Sam Braun, a friend of her mother, is a surrogate uncle to Catherine during her childhood and stormy teenage years. While they operate on opposite sides of certain gray areas of law, they share a lasting affection and grudging respect. Catherine learns that he is, in fact, her biological father after performing a DNA control test during a murder investigation involving Sam. This comes to haunt her during the trial. When Sam dies, he leaves Catherine and her mother some of his fortune, but the vast majority of it is tied up in the land development trusts he began during his life.
Catherine, while well-liked and highly successful at her job, seems to be trailed by bad luck in her personal life. Grissom is known to have criticized her for having a personal life at all, as drama seems to find her despite her best intentions. Her dates seem to end up jeopardizing investigations, or involved in them. Her daughter was kidnapped as a warning to her, and soon after her safe return, her father was killed in her arms by the kidnapper. Her recent dating life is next to nil, though she shares an unresolved, and ultimately tragic, flirtatious relationship with her co-worker, Warrick Brown.
While not vain in the strictest sense, Catherine has a dancer's strong sense of beauty and style to go with her natural good looks. She has watched her mother age from a great beauty into comfortable older-middle-age, and as she watches Lindsey grow up, she is often shown to be struggling with her own signs of aging.
In mid Season Nine, upon Gil Grissom's retirement, Catherine was promoted to Shift Supervisor of the graveyard. After a year of difficult changes, during which several team members came and went, she took the counsel of her friend and colleague Sara Sidle, and appointed Nick Stokes as her Assistant Supervisor: someone to act as a buffer, and bridge the distance between Catherine and the team. Season Ten shows Catherine rising to the challenge of her hard-won position, and commanding a team that balances experience and skill with fresh new energy and insight.
Season Ten also shows Catherine entering into a romantic relationship with Lou Vartaan, an LVPD Detective who has assisted the CSI's many times over the years. Beginning with a conversation about their respective nearly-grown children, the two are shown to have a volatile partnership, from difficult discussions to passionate encounters, but always in one another's corner. When Vartaan is badly injured on the job, Catherine immediately goes to him in hospital, obviously prepared to stay for the long haul, seemingly a mild surprise to both.
After members of her team turn rogue during the Los Angeles climax of a year-long manhunt, Catherine is demoted back to Assistant Supervisor. She now works under a new Supervisor, DB Russell, a recent arrival in Vegas. With the entire team on edge from a difficult case and a change of management, Catherine now faces the task of being the buffer between her old friends and co-workers, and a boss she isn't sure she can work with.
In 2012, after a particularly harrowing case involving a childhood friend and the violation of her own home, Catherine came to a crossroads in her personal and professional life. Accepting a surprise offer of a position within the FBI, she stepped away from her old life - away from the colleagues who had grown as far as she could mentor them, away from her adult daughter who no longer needed her so near, and away from Vartaan, who she realized wanted more than she could give. And perhaps most importantly, away from the family history and personal skeletons that have kept her tied to Vegas her entire life. As far as mid-life crises go, Catherine's is perhaps among the more positive.