Credit: Tony Barson/WireImage

Jason Priestley will help CSI celebrate its 300th episode on Oct. 23.

The former Beverly Hills 90210 star will make a guest appearance in the episode as a casino mogul. Here’s the deal: He once threw the most lavish parties in Las Vegas, until a scandal tainted his reputation and now he’s a recluse. He is the heir to a classic movie studio empire, a lover of film magic, and apparently he’s looking to believe in his dreams again!

Marg Helgenberger — who will co-star opposite Josh Holloway in the new CBS drama Intelligence on Feb. 24 — will also reprise her role as Catherine Willows for the 300th episode.

CSI returns Wednesday, Sept. 25.