9-10PM · Showtime · Returns Sept. 28

Dexter's big discovery last season — that his foster father Harry committed suicide — serves as the catalyst for the thriller's third go-round. ''He's not living according to anyone's rules but his own,'' says Michael C. Hall of his titular character. ''He's claiming Harry's code for himself.'' That code — don't kill innocent people! — is compromised when Dexter accidentally violates it in the first episode, causing a ripple effect that will last the entire season, when the incident catches the attention of an ambitious assistant DA (Jimmy Smits). ''These two unlikely types,'' reports exec producer Sara Colleton, ''form one of the most unusual friendships we've ever had on our show.'' Watch out, Jimmy: Dexter's ''friends'' don't typically have lengthy life spans.

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