Marg Helgenberger of CSI taped her last episode in the middle of season 12, amid bargaining and season changes. "CSI: Crime Scene Investigation" is bringing Marg Helgenberger back for a huge milestone for the popular series. Marg Helgenberger will return to the CSI for its 300th episode.

The network said Marg Helgenberger will return to CSI as her original character, forensic scientist Catherine Willows, to help the CSI team break a cold case that has had them baffled for more than 10 years.

According to CBS, Marg Helgenberger’s CSI episode will have the team probing a murder in the home of a former casino mogul who has gone into seclusions. The CSI team considered him a suspect in a similar crime in 2000.

Marg Helgenberger’s CSI last episode happened last year after "CSI" had been on the air for twelve season. Marg Helgenberger CSI Last Episode aired on Jan. 25, 2012 and was titled "Willows in the Wind."

Marg Helgenberger was one of CSI’s original stars.

Don McGill, executive producer of CSI, said "We were just really excited to have Marg come back because, obviously, she's such an important part of the history of CSI. And she was super excited. It was kismet!"

McGill said The CSI episode will focus on a cold case that "takes our characters back to the beginning. They have to investigate a murder with the same M.O. and the same suspect from 14 years ago."

Marg Helgenberger's CSI will happen partially in flashback. McGill explained "We will flash back 14 years to seminal moments that show Catherine, Nick (George Eads), Sara (Jorja Fox), Greg (Eric Szmanda) and Ecklie (Marc Vann) as they were, [and how that] informed the evolution of the characters now. It's going to be a really fun episode, very emotional, that honors 14 years of CSI."

"CSI" will return for its 14th season on Wednesday, Sept. 25, at 10 p.m. ET. The Marg Helgenberger-starring 300th episode will air Oct. 23.