Marg Helgenberger) is back in Vega$ Baby. The actress is going to appear in the big 300th episode of the Original CSI. Wow it's hard to believe that this show will soon be airing episode number Three Zero Zero. Marg left the show last season fortunately she left under good circumstances and they didn't kill her character off. Crime Drama TV shows have a tendency to kill off characters of actors who voluntarily leave a show before the end of its full run.
So far no real details have come out except to say that Catherine returns to help the CSI team solve a 14 year old cold case. So they close a case from before the series began in the fall of 2000.
Marg Helgenberger to return for 'CSI' 300th episode - CBSNews
'CSI' 300th episode: Marg Helgenberger set to return - Entertainment Weekly
Helgenberger back for 300th 'CSI' episode - Chicago Sun-Times
Marg Helgenberger returns to 'CSI' for 300th episode - USA Today