CSI: Crime Scene Investigation may have gone through a few cast changes in the last few years, but long time fans will be rewarded tonight when Marg Helgenberger returns to the team for the 300th episode.

Titled "Frame by Frame," the milestone episode will feature several flashbacks as the Las Vegas investigators work to connect a current case to one that occurred 14 years prior.

"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," series creator Don McGill told TV Line. "It's going to be a really fun episode, very emotional, that honors 14 years of CSI."

Helgenberger will reprise her role as Catherine Willows while Jason Priestley (Beverly Hills, 90210) will guest star as a reclusive casino mogul named Mr. Witten, according to Entertainment Weekly. It is possible that the rundown, dilapidated casino featured in the opening will belong to him.

"Ext[erior] Premiere Casino - Night: Dive down to the entrance of the casino. Hear a distant, ghostly voice of the concierge, welcoming casino guests," reads the direction for the opening shot, as posted by the CSI Writers' Room. "Int[erior] Premiere Casino - Night: Push through the Hollywood-themed Casino. Something's odd...it's spooky, desolate. Move over empty roulette table. It's still, but we hear the wheel spin, ball clacking."

E! warns viewers to keep their eyes peeled for a few Easter eggs. The number 300 will reportedly be hidden in the episode 14 times.

CSI airs Wednesdays at 10 pm ET on CBS. Check out a preview for tonight's episode in the video below.