On tonight's all-new episode of "CSI," the team investigates a mysterious illness that is killing random people in Las Vegas -- and ET has the dish from the hit show's stars, Marg Helgenberger and Laurence Fishburne!

Laurence tells ET that on the episode, victims of the mystery disease display "tweakingly aggressive behavior," and Marg says that her character Catherine might be in for a battle with one of the infected! "We do so many kind of cerebral things on show," Marg says. "It was just really fun to do action again."

Catch the all-new episode of "CSI" tonight at 9 p.m. on CBS.