Marg Helgenberger will return to 'CSI' for show's 300th episode Catherine Willows (Marg Helgenberger) on her last episode of "CSI: Crime Scene Investigation." Marg Helgenberger's last episode. August 21, 2013, 4:04 p.m. Marg Helgenberger is returning to "CSI" next season. For one episode, at least. One of the original cast members of the long-running CBS procedural, Helgenberger recently announced via Twitter that she was coming back for the show's 300th episode, which is set to air this October during "CSI's" 14th season. On Tuesday, Helgenberger wrote, "Very excited to see my pals @CSI_CBS for the 300th." Helgenberger was originally teamed with William Peterson when the show began in 2000 and stayed on through the arrival of two other leading men: Laurence Fishburne and Ted Danson. She left the show midway through its 12th season. Her character, Catherine Willows, a crime scene investigator supervisor and forensic scientist, accepted a job with the FBI. However, at the time of Helgenberger's departure from the show, she made it clear that she would be open to returning from time to time. "You haven't seen the last of me," she told the Associated Press in 2012. The new season of "CSI" begins Sept. The time Louis C.K. found a dead body in the East River Martin Luther King Jr.'s 'Meet the Press' visit will be re-aired Appreciation: Elmore Leonard's unique voice lives on in 'Justified'