Reliable insiders tell me—and the CW confirms—that James Marsters (swoon, Buffy's Spike) is returning for four episodes of the superseries during the new season.
We last saw Marsters's character, Dr. Milton Fine (aka Brainiac), in Smallville's fifth season finale.
While it's unclear exactly how James is returning, I can tell you he's reprising the exact same character, he's returning to set very soon and his episodes begin airing in January. He also appears on CBS' Without a Trace this season."