Not all voice-overs are created equal.

Kristin Bell helps set the snarky tone of The CW's "Gossip Girl," and Brenda Strong adds gravitas to ABC's "Desperate Housewives."

But neither is asked to do what Michael C. Hall, star of Showtime's "Dexter," does every episode: invite viewers to listen in on the thoughts of television's most sympathetic serial killer.

"I think [the voice-over] reinforces the sense on the part of the audience that we're seeing things from Dexter's point of view, that we're in on a secret that no one else in his world is, and as a result have an intimate relationship to him and are perhaps, just by continuing to watch, knowing what we know, implicated and complicit," Hall said in a phone interview last month.

It's a relationship the actor takes seriously, recording a preliminary version of the character's thoughts on a recorder in his trailer during the filming of each episode, for the use of the show's editors, then rerecording later to match to specific shots and scenes.

"Early on, you know, there was the thinking that I'd just record it and they'd lay it in there. And I really lobbied to take the time to rerecord all the voice-over to picture each time . . . It's sort of relinquishing a little less control, or taking a little more control," said the actor, who's also an executive producer on the show.

Control's an issue as well for Hall's character, Dexter Morgan, a blood-spatter specialist who moonlights as an extremely tidy vigilante, choosing his victims according to a code laid down by his late father, Harry (James Remar), a cop who sought to give his disturbed son what he considered an acceptable outlet for his homicidal tendencies.

It's Harry's voice Dexter himself most often hears whispering in his ear, perhaps more often than usual this season, the show's fourth, and so far, its highest-rated.

As Dexter wrestles with his own introduction to fatherhood, and stalks another killer -- code-named "Trinity" and played by John Lithgow -- who appeared at first to have managed the work-family-murder balance Harry always claimed was never possible, it may be time to ask just what kind of father Harry was, anyway.

"The idea of rehabilitation seemed to be off the table for Harry, and that's an outside-the-box way of approaching things," Hall said wryly.

"As with many, if not all things on 'Dexter,' there's a light and a dark side to it," he said. "The idea of a father shining a light on Dexter's deepest darkness and telling him that he loves him, not in spite of it, but perhaps even for it, is a beautiful thing in a way. And at the same time it's pretty twisted" that he encouraged him to kill people he thinks deserve to die.

"I think Harry himself, as a cop, I think, had come up against injustice after injustice in his line of work and maybe was a frustrated vigilante in his own right. And was able to exorcise some of those demons, or act out some of those impulses, through his uniquely afflicted and/or gifted son," Hall said.

Lithgow's character, whose seemingly idyllic family life was revealed to be anything but, didn't share a scene with Dexter until several episodes into the season, and "I think it's nice that they created that tension," Hall said.

"When we did finally meet and start to share scenes together, I mean, it was thrilling. John is an actor I've admired for most of my life. And along with his formidable talent and intelligence and all of that, he brings such a sense of play to the table.

"There was really a sense of play that accompanied the scenes we had together. The relationship that we were called upon to simulate was so insane that it was really just a lot of fun. I mean, we laughed a lot, you know, when 'cut' was called," he said.

With the Dec. 13 season finale just a couple of weeks away, a fifth season's already ordered. Season 4, meanwhile, is breaking ratings records for Showtime. Viewership so far has peaked in the Nov. 1 episode, whose 9 p.m. Sunday airing was watched by nearly 1.9 million viewers. With repeats, the series averaged more than 3 million viewers a week in its first seven episodes, the most recent for which complete numbers are available.

But could someone like Dexter even exist? And if so, how long can he continue?

"I wondered if he was a person who could ever be when I first encountered him, but of course now he just exists in the form of these episodes," Hall said.

"I do think that things resolve in a way this season and do set the stage for us to really move into new places. But you know it can't go on indefinitely. We finished the first season and I thought we should probably just stop, and had no idea what we were going to do," he said.

And then, "the bodies surfaced immediately at the top of the second season. I thought we'd spend all this storytelling capital by the time the second season [was] over," but no.

"I think we have incredibly imaginative writers who manage to drum up new . . . organic-seeming conflicts and challenges for the character that move him forward and sort of force him into an experience of himself or at least a more sophisticated simulation of himself as more human," Hall said.

"With the momentum that the show continues to generate, it's hard to say that that would be our final season. Maybe we'll do more than that. I don't know -- if Dexter gets caught, I mean, do we want to watch Dexter in prison? Do we want to watch Dexter in a courtroom? I don't know."

TV columnist Rob Owen's Tuned In+ is featured exclusively on PG+, a members-only web site from the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.