“Dexter” has gone from cult show to mainstream success in two seasons. Showtime’s dark drama about a Miami serial killer who works for the police, was rewarded with 2008 Emmy nominations for Outstanding Drama Series and Outstanding Drama Actor (the brilliant Michael C. Hall). CBS, which owns Showtime, repeated Season 1 for a network audience. Season 2, now out on DVD, is a riveting follow-up to the sensational debut season. Dexter’s stash of dead bodies turns up, and the FBI, led by special agent Frank Lundy (Keith Carradine) and assisted by dirty-talking but adorable sister Deb (Jennifer Carpenter), is on the case. Suspicious Sgt. Dokes (Erik King) is also on Dexter’s trail. Lila, a sexy and dangerous British babe (neatly played by Jaime Murray), drives Dexter to the breaking point. All in all, great writing, solid acting, bright South Florida colors, another killer season. You will race through the 12 episodes. But don’t look for any cool DVD extras; there aren’t any, just episodes of other Showtime series. Season 3 begins Sept. 28. Jimmy Smits joins the cast as an assistant district attorney. A trailer is up on the website.