Heroes Reborn type TV Show network NBC

Why aren’t more of the original Heroes returning for NBC’s upcoming event series? In short: story and scheduling.

“Some of the people, some of the actors, did not have the availability because they were involved in other things,” Heroes Reborn executive producer Tim Kring said at the Television Critics Association’s semi-annual press tour, noting that while that aspect was beyond their control, bringing back alums was ultimately storyline based.

“The story was really the thing that dictated who would come back,” he continued. “The show was always designed to be very elastic in its premise. I always saw it as a show that could repopulate itself. I wanted to make it something that was easy for brand new viewers to watch. For them, caring about new characters is just as important as having former cast in the show.”

As previously announced, returning stars for the 13-episode event include Jack Coleman (H.R.G.), Masi Oka (Hiro), Sendhil Ramamurthy (Mohinder), Jimmy Jean-Louis (the Haitian) and Christine Rose (Angela Petrelli). The new cast includes Ryan Guzman, Robbie Kay, Danika Yarosh, Judith Shekoni, Kiki Sukezane, Henry Zebrowski and Gatlin Green.

A year prior to the show’s debut, a terrorist attack in Odessa, Texas, resulted in those with extraordinary abilities going into hiding from those who seek to avenge lost loved ones in the incident—that’s where Zachary Levi’s character comes in.

The attack is one of the main reasons why Hayden Panettiere is not among the returning cast members. “In the real world of the story, [her character Claire Bennet] died a year prior to our story starting,” Kring said. “That gets into some of the mythology that’s attached to the original show.” In that regard, her father H.R.G. will act as a guide for new viewers in unveiling some of the backstory from the original run.

Viewers of the original may be interested to hear that Reborn picks up in real time, five years after Claire went public with her abilities. “It was almost an obligatory baton pass to where we needed to go from there,” Kring recalled of the series finale. “Because we didn’t get to have that fifth season, I did always have that in my mind that there was an unfinished nature to it… This world has become a very different place. There’s something really great about this: This is not the fifth season, this is actually the 10th season as if there were seasons in-between. I had always wanted to tell the story of when the world discovers these people.”

Heroes Reborn will now premiere as a two-hour event on Thursday, Sept. 24 from 8 to 10 p.m. ET on NBC.