What happens when the fifth cylon drops by CSI? Fans of both Sci Fi Channel's Battlestar Galactica and the long-running CBS procedural will get that answer when Kate Vernon (aka Ellen Tigh) guest-stars on CSI this April.

"It's a really fun episode," Vernon shared with me during a recent visit to the TVGuide.com offices. "I play a professor of media theology, and I'm making a documentary on the Gestalt constructs of sci-fi mythoculture."

(Yes, that is a mouthful, but luckily Vernon was well-rehearsed in explaining it.)

As the CSI episode unspools, a murder of course takes place, and an investigation follows at a Comic-Con-type venue. Along for the ride are no less than a pair of BSG scribes, director Michael Nankin and exec producer Ronald D. Moore (in a fleeting cameo). Says Vernon, "It's a little wink to Battlestar."  

Learn more about it in the video below.

Of course, the main reason for Vernon's visit was to promote the utterly unpredictable series finale of Battlestar. Get the tease-filled scoop from her in this second video.