Robert Knepper and Masi , Heroes

Heroes kicks off November sweeps Monday with the reunion of one of the show's most memorable, if tragically separated, couples: Hiro Nakamura (Masi Oka) and Charlie Andrews (Glee's Jayma Mays).

Check out photos of the Heroes cast

The duo's brief love affair began in Season 1, but was brought a drastic halt when Sylar (Zachary Quinto) split Charlie's skull to steal her power. Hiro later traveled back in time to prevent Charlie's murder, and though he was successful, she eventually died from a blood clot in her brain. Now facing his own death by brain tumor, Hiro has set out to cross Charlie's name off his bucket list by saving her once and for all. So, will the third time be the charm?

"I think Hiro's learned a little bit more about what he can and can't do," Oka tells TVGuide.com. "There's definitely something he knows and there's the people he's met as well. He's tried over and over again to save Charlie, but this time he has different kind of knowledge that definitely will help out."

Mays says her character desperately wants things to work out, but she admits that she's not sure if this will be the final chapter in the Hiro-Charlie story. "Charlie has a deep love for Hiro, and she wants to further that relationship," Mays says. "But she also wants to make a difference in the world somehow. I've always interpreted it is as the perfect relationship for Hiro and for Charlie. So, I know that people are really rooting for them."

Keep up with our weekly recaps of Heroes

Oka says there will be plenty of surprises along the way (keep your eyes peeled for Isaac Mendez!), and he promises a Hiro-Sylar showdown. But Oka also hints that Hiro's mission is much bigger than that one battle. "This is a big homage to the episode where we see Charlie's head get cut off," Oka says. "This is kind of the side story of what could have happened behind the scenes. It's more than just saving her from Sylar because she was destined to die. Now he knows what the problem is, so maybe he can find someone to help out with that."

Some-one? Although Oka would not specify who comes to the rescue, he says mysterious carnival leader Samuel (Robert Knepper) does have a part to play. Could Hiro's mission have some impact in Samuel's master plan?

"He definitely has a bigger scheme," Oka says. "We find out why he's there by the end of the episode, but Hiro is just dancing on the palm of his hand in some senses. Samuel also has a past that needs some fixing, and the only person who could probably help him is Hiro. So we'll see how everyone's destiny mixes around with the paths that have been taken."

Robert Knepper lets us inside the head of Heroes' new villain

At the very least, Samuel teaches Hiro that it's possible to change pieces of the past without altering the entire future. Or is it? "What Samuel says to Hiro is maybe not his true purpose for being there," Knepper says. "Samuel has imparted that piece of wisdom that if you take one little thing and change it, it really doesn't matter. So what's the ulterior motive for changing one little thing? For Samuel, it's probably something big. For Hiro, Samuel wants to convince him it's smaller, that he can get away with it."

But let's not forget that while Hiro is out saving the day, he's also dying. Oka says Hiro will come to grips with the possibility of death in this episode. "He doesn't really try to save himself. He accepts his death in some senses, and makes sacrifices to help Charlie out," Oka says, adding that his character's fate still hasn't been decided. "Whichever way we go, I don't want to cheat the death. We're asking people to go on this emotional journey with Hiro, and if it ends in death, we don't want to just say, 'Ha ha, it was just a magic trick.'"

Whatever happens between Hiro and Charlie, Oka says Monday's episode sets up the next few miles in Hiro's journey. His death — or at least the focus of the bucket list — will be put on hold. "Charlie was definitely the highest thing on his list, and we may get back to that. But right now, let's say he's kind of a prisoner," Oka teases. "He gets stuck in a grander scheme."

Heroes airs Mondays at 8/7c on NBC.