"It is, without a doubt, the most fundamentally game-changing development as we've had since we started telling this story," says Michael C. Hall, whose "Dexter" launches its seventh season at 9 p.m. EDT Sunday on Showtime.
At the end of season six, the title character was finally compromised. Just as he slices into his latest victim, Debra (Jennifer Carpenter), Dexter's sister, walks in and catches him in the act.
She's horrified to see her brother in the situation. He's shocked to have her, his most trusted confidant, finally learn that he's a killer.
The scene will set the tone for the final two seasons of "Dexter," supposedly ending in 2013. (The ending is also noteworthy for Showtime, which says "Dexter" remains its most-watched series and one of its most acclaimed.)
"One of the things that we've always been able to count on is that Dexter's secret is his own," Hall told reporters recently, "and it's not anymore. It's been so invigorating to play these scenes, to be preoccupied in ways that Dexter's never been required to be preoccupied."
The secret revealed isn't the only new development. Ray Stevenson will join the story in episode six as a European mob boss.
Dexter has been compromised before -- just not to this degree. He's had co-workers and foes stumble upon his secret of a double life: forensics expert for the Miami-Dade Police Department by day, serial-killer avenging angel at night.
From Carpenter's end, the scene in which Deb catches Dexter was startling to play.
"It was all I needed to just sort of step away, and I didn't have to manipulate anything," she says.
"It was all right there. It was like the strangest, scariest seduction scene in a weird way.
"And the first time, in a really authentic way, I felt my power ... I felt like I felt as weak and as powerful as I've ever been as an actor and in the character."
Now, with the sister finding out, Hall is captivated as an actor.
"Dexter is never more compelling than when he is in trouble, and he's never been really in deeper trouble than he is now," Hall says.
Wherever that may lead for the character, Hall views it as the endgame of the story.
"There's a feeling of arrival, you know, that we've earned this arrival and this new landscape," Hall says. "In a lot of ways, it feels as rich as it ever has."
Other highlights for the week of Sept. 30 to Oct. 6 (all times EDT; listings subject to change; check local listings):
-- "The Simpsons" (8 p.m., Fox). The Springfield family begins its 24th season by going to New York City, where Bart tries to reconnect with a girl from his past who has reinvented herself.
-- "The Good Wife" (9 p.m., CBS). Diane and Will try to save the firm from financial ruin as the fourth season comes to order.
-- "Homeland" (10 p.m., Showtime). Trying to reclaim her life and career, Carrie (Claire Danes) goes on another dangerous mission while dealing with electroshock therapy and a chemical imbalance in the season-two opener.
-- "Marie" (Noon, Hallmark Channel). Marie Osmond returns to daytime TV, this time with home-improvement expert Paige Davis.
-- "I Heart Radio Music Festival" (8 p.m., CW). Highlights from this year's event include performances by Taylor Swift, Pitbull, No Doubt and Pink.
-- "Hart of Dixie" (8 p.m., CW). Zoe starts season two torn between George and Wade and by befriending a guy the rest of the town is giving a cold shoulder to.
-- "Animal Intervention" (9 p.m., Nat Geo Wild). In this new series, interventions are conducted for out-of-control wildlife owners who can't see they aren't doing their animals any favors.
-- "Supernatural" (9 p.m., CW). Sam and Dean reunite after a year apart, but the meeting isn't smooth in this season-eight opener. Sam's not sure he wants to give up his idyllic life to join Dean on another adventure.
-- "Presidential Debate" (9 p.m., various networks). President Barack Obama and Republican presidential nominee Mitt Romney talk about domestic policy in the first of three debates, this one live from the University of Denver.
-- "Life After Top Chef" (10 p.m., Bravo). Three past "Top Chef" favorites have their lives documented after the show to see where they are headed professionally and personally.
-- "30 Rock" (8 p.m., NBC). The gang returns from summer hiatus, only to be disheartened by Jack's poor fall programming decisions as season seven takes off.
-- "Parks and Recreation" (9:30 p.m., NBC). Lucy Lawless ("Xena: Warrior Princess") plays Nick's new love interest as season five begins: a single mother with an ax to grind against the parks department.
-- "Gabriel Iglesias Presents Stand-Up Revolution" (10 p.m., Comedy Central). The comic presents a second season of standup and improv talent.
-- "Pit Bulls and Parolees" (10 p.m., TLC). In New Orleans, a woman who rescues pit bulls and pairs them with parolees sees how lives are transformed by her program. The fourth-season premiere.