'CSI' Celebrates 300 Episodes (PHOTOS)

After 13 seasons of solving crimes, "CSI's" 300th episode will air in October.

Featuring "Beverly Hills 90210" alum Jason Priestley and the returning Marg Helgenberger, the episode will hit CBS on October 23. While not much is known about the plot, Priestley will appear as a casino mogul who who "once threw the most lavish parties in Las Vegas, until a scandal tainted his reputation and now he’s a recluse," according to EW.

Additionally, Helgenberger
-- who left the series halfway through Season 12 -- will return in a series of flashbacks, according to TV Guide.

Click through the slideshow below to see photos from the "CSI" 300th episode anniversary party.

CSI 300th Episode

"CSI" Season 14 premieres Wednesday, Sept. 25 at 10 p.m. ET on CBS and the 300th episode airs Wednesday, Oct. 23 at 10 p.m. ET on CBS.

CSI Season 13