Rachel Bilson, of “The O.C.,” guest stars on “Chuck” tonight. Bilson throws a wrench into the works when she shows an interest in Chuck (played by Zachary Levi). Of course, he can’t jeopardize his fake relationship with Sarah (Yvonne Strahovski) to pursue Bilson’s character, but there’s likely to be some chemistry and a possible love triangle.

According to executive producer Josh Schwartz (via Kristin Dos Santos at E!), “Rachel Bilson, right now, is only scheduled to do two episodes. [But] she had a really great time. I think at first she was like, ‘Oh, I don’t know, I just got out of a TV series.’ But maybe we could lure her back.”