Apparently, NBC spy comedy Chuck knows how to keep up its geek cred. They're casting Tricia Helfer, AKA Battlestar Galactica's Six, as an agent assigned to replace the increasingly (romantically-)compromised Sarah and keep the problematic Mr. Bartowski out of trouble in the second half of the show's second season. But will her spine end up glowing when she falls for Chuck's nerdish charms?It seems that Helfer can't quite shake the spy-juice out've her genes following her four episode stint on Burn Notice earlier this year; according to Entertainment Weekly's Michael Ausiello, she'll make her Chuck debut as Agent Alex Forrest in the season's eighteenth episode. The character is described as "a by-the-book ass-kicker... who shows no fear, no remorse and, much to Agent Casey's delight, is very easy on the eyes," but fans of the Chuck/Sarah melodrama shouldn't worry; Helfer is apparently only signed on for one episode. Unless, of course, she proves popular enough to bring back for a longer run... Ausiello also spills the beans that Chuck is about to get a rival himself; British actor Jonathan Cake is to join the show as an MI-6 agent who'll be the latest character to step into the vacant spot on the eternal Sarah-Chuck-[Your Name Here] love triangle. And, unlike Helfer, Cake is apparently signed on for multiple episodes. 'Chuck' Exclusive: Helfer in! Strahovski out? []