To conclude the first season of “Fringe,” co-creator J.J. Abrams says tonight’s episode is “major turning point in the long-term arc of the series.”

Fans who want to go into the story unaware of what will happen in tonight’s episode, airing at 9 p.m. EST on FOX, may want to skip to our next story.

As has been previously reported, actor Leonard Nimoy will feature on tonight’s episode in the pivotal role of William Bell.  The episode will also bring back some other familiar faces including Robert Jones.

Abrams said that he and the writing staff have worked all year to ensure that the series is accessible to fans who don’t tune in for each new installment but also offers rewards to viewers who faithfully watch the series.

“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,” Abrams told SciFi Wire.  “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.”

“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,” he continued. “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.”

And what about the highly publicized cameo by Nimoy?

“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,” Abrams said.