A severed head takes the CSIs to a go-cart rink as they search for a killer.

The CSI team investigates the suspicious death of a go-cart racer who took his hobby to the highway, when a severed head rolls through tonight's episode of "CSI: Crime Scene Investigation," airing at 9 p.m. on CBS.

Then the murder rate doubles when the team gets a second case -- the murder of a HUGH HEFNER-like publisher at a hip new restaurant where customers dine in the dark.

Dining in the dark isn't something that series star MARG HELGENBERGER, who plays Catherine Willows, is interested in. "I want to see what I am putting in my mouth," she tells ET's JANN CARL, who is on location with the hit CBS series at a go-cart rink.

"The best part about it is we are all here on one day," says GARY DOURDAN (Warrick Brown), who was competing with GEORGE EADS (Nick Stokes) to see who could bump each other harder. "That is pretty rare. Those are nice days."

The best part of the episode for many fans may be the return of Sara Sidle (JORJA FOX) to action, following her near-death experience in last week's season premiere.

"Coming into episode two, Grissom (WILLIAM PETERSEN) or Sara have been invited not to be on the night shift anymore," Jorja reveals. "Sara has decided it should be her who should leave and go to the swing shift ... For Sara, the idea of not working with Grissom anymore is devastating. The only friends she has are on this shift, so after the most devastating thing [that happened] in her life, she is going off alone."

In real life, the hardest part for Jorja was having to keep the secret of whether or not she survived her attack by the miniature killer.

"I lied to my own family," she admits. "[I said,] 'I don't know anything.' It was hard, but what was great about it, too, was there were people that actually wanted to know."