J.J. Abrams, co-creator and executive producer of Fox's sci-fi series Fringe, told reporters that tonight's season finale provides a "major turning point in the long-term arc of the series."

The episode, "There's More Than One of Everything," will feature the return of the mysterious David Robert Jones (Jared Harris), the disappearance of Walter Bishop (John Noble) and a scene between Olivia Dunham (Anna Torv) and William Bell (Leonard Nimoy), Walter's old partner and co-founder of Massive Dynamic. Abrams spoke during a conference call with reporters last Friday. The following are edited excerpts from the conversation. The season finale airs at 9 p.m. ET/PT.

Take us through the discussions that resulted in Leonard Nimoy coming on board for the season finale.

Abrams: I believe it began with an e-mail that I sent to him. No, no, here's what happened. I remember. I called him and just essentially started begging. I told him we were doing this show. He was familiar with it, but I don't think he'd seen it. He knew the show, and I basically explained that there was a critical character who had been mentioned throughout the first season, including the pilot, and it was a big deal for the show, not just where he came from and what his backstory was, but where he was going. And [I said] it'd be an obvious honor if he would consider playing the part. He was open to the idea, but he wanted, of course, to see the show and read some pages. So we sent him everything that we could, and I was thrilled when he called back, and he thought it was intriguing and interesting. That was how we actually ended up getting him to return to the role of Spock in Star Trek, where we told him the idea, pitched him the thing, and his response was interest and intrigue, and I knew that was a good sign.

What can you tell us about the season finale?

Abrams: I can tell you that in the story of Fringe it is the end of one chapter and the beginning of another. If you look at this show as a series of stand-alone episodes, I think it even works in that regard, but because we're trying to do both—have a show that you can tune into any time and get a Fringe fix or you watch regularly and sort of ride the wave of the overall story, and see how things connect and fit together that you might not otherwise expect to—this feels like it is definitely one of the tentpole episodes in the mythology of the show. The first season really was about the setup of this world, the characters, their roles, their jobs, and as the show went on I think we got more of a handle on their interactions and getting a sense of the rhythms of the show. But this is really a massive turning point in the long-term arc of the series.

Olivia [Anna Torv] really seemed to lighten up a little bit as the show progressed. In general, how much did you have planned in advance, and how much of what we've seen was simply the show finding itself as you went along?

Abrams: We actually had a surprising amount planned in broad strokes, but the crazy thing is, as you work on it, you start to get resistance, not from an actor, not from a director or even other writers on the show, but a show just sort of defines its shape in a strange way. One of the things I love about the show is the inherent humor in the insanity of it. If the show takes itself too seriously, then I'm afraid people will laugh at it, but if the show has humor inside of it, then the show itself is embracing and admitting to the preposterous nature of many of the episodes and stories. I love preposterous stories. My favorite movies, if you look at Jaws or Alien or Tootsie, ... there are movies that if you describe the story, you go, "What? All right. OK." But done well, you go, "Oh, my God, that was the greatest ride ever." So, for me, the humor did, I think, increase as the season went on.

I think things like bringing in Olivia's sister [Ari Graynor] began to give her at least opportunities to be warmer to someone. She's a character who admitted in the show that she doesn't really have friends. So I think the story for Olivia over the course of time is one of a guarded, protective woman who, over time, is in a sense forced to be more vulnerable. And you'll see, something definitely happens next year. But it is an evolution for her.

If we were to say that season one was about meeting the characters and the characters meeting the enemy, how might you describe what you're planning for season two?

Abrams: I would say, yeah, I think the first year was about, not seeing the enemy, but getting to at least understand that there is an enemy. I would actually argue that, in a way, season two is getting to know the enemy. Season one is identifying that there is an enemy and really getting to know each other. But I think that as the show progresses what you'll see in the second season is that it's building to a very specific type of confrontation, and I think you'll see that there will be a really interesting shift in the fundamental paradigm of the show at the beginning of next season, in a very cool way.

Without going into any details about it, it has a kind of fun, fresh way in next year that I think is ... you never know how it's going to work. You just cross your fingers and pray people like it, but I feel like it's one of those next-season beginnings that feel thrilling to me in a way that's more than just "Oh, I can't wait for them to come back." It's "I can't wait for them to experience what we're doing and for them to come back this way." I know I'm being insanely vague, but I would say the excitement is not just now in these characters knowing each other, but it's with playing with that a little bit.