Dexter has done some wonderful things with guest stars. Recall with awe a John Lithgow who still provokes nightmares (albeit, very articulate nightmares). On the other end of the spectrum, last season's Lumen (Julia Stiles) arc was not exactly a masterpiece. It seems as though this season hasn't soured on the idea yet, as a whole bunch of new castmembers are being brought in for multi-episode arcs. The latest addition is Jordana Spiro.
The film and television actress (Harry's Law, The Goods) will join Dexter as a disciple to a previously mentioned new character played by Edward James Olmos, who is being set up as the season's central villain. Olmos' right-hand man will be played by Colin Hanks. And somewhere in all of this, they're managing to fit in Mos Def.
As the season's theme will be religion and spirituality (expanded upon in this Behind the Scenes Featurette), it seems as though Olmos' teachings will represent a "cult" that has Hanks and Spiro brainwashed into doing presumably horrible deeds. Spiro, however, does not enter the action until late in the sixth season, which suggests that her role will come with a healthy amount of mystery (and importance, as all the really big stuff happens at the end of the seasons).
Dexter's sixth season, will premiere on Showtime on Sunday, October 2 at 9/8c, clearly with a healthy promise of the horror we know and love.