Even longtime viewers of CSI were surprised at the revelation at the end of last season that the characters of Grissom and Sara - played respectively by William Petersen and Jorja Fox - have been involved in a relationship for some time. Now, the biggest mystery on the show doesn’t involve the victim of the week, but how long that relationship has been going and how they’ve managed to keep it quiet all this time? At the TCA press tour yesterday, Fox came clean to Now Playing on where the storyline came from and where it’s going in season seven.

“I think one of the coolest things about it, and the way that the story ended up being delivered at the end of the season - and [it was] quite really brilliant, as I think the writers are - is that we suddenly find these characters together, and we know not how long this has been going on,” Fox said. “And I think that was a really brilliant way to do it. I think it’s going to open a lot of ideas for the characters.”

Coincidentally or not, ABC has moved ratings powerhouse Grey’s Anatomy into the Thursday night timeslot opposite CSI this season. Earlier in the press tour, CBS president Nina Tassler told critics that CSI is in the surprising position of being the underdog, and she’s expecting the series to “get dinged” by the move. Unsurprisingly, there will be a drive this season to do more personal stories than ever before to retain viewers who might be more interested in the romantic entanglements between Meredith and McDreamy than DNA testing and autopsy reports. But in an interview after the panel, Fox pointed out that the idea to show the relationship came about before the move was announced.

“Grey’s is very celebrated for a lot of good reasons,” she said. “One of them has a lot to do with the personal lives of their characters. The good thing I can say about Sara and Grissom is that idea started before we knew we were going up against Grey’s. I mean, obviously the Sara-Grissom thing has gone on for six years, but the idea to bring that to light happened before we knew we were going to be up against Grey’s. So I think there will be very little about our show that will change. I don’t think we’re going to be more like Grey’s. I think that would be very foolish of us to do.”

The direction has already drawn strong fan reactions on both sides. The controversy has caused Fox to feel a little apprehensive going into the new season, something she hasn’t felt on CSI in a long time. “I was really nervous, because you’re so invested in characters,” Fox said. “I think it’s a cool storyline and it’s untraditional; it’s slightly taboo, it’s slightly scandalous. There’s a million reasons to love it as an actor, to tell the truth. I love working with Billy [Petersen]. Obviously, the first two seasons we worked a lot together. I actually couldn’t stand him for the first few months we worked together. And he knows that, so I can tell you that. And I really thought, ‘How am going to make it through this show? I don’t even like this guy.’ And something happened right around December, where we pushed through something. I don’t think he liked me that much either, to be perfectly honest. And all of a sudden we found this rhythm and this place. So it’s really exciting to get to take it on.”