By Dani Nick

Philadelphia (CW Philly) — Now in its fifth season, The Flash has taken viewers on Barry Allen’s epic journey for 99 episodes. TV Guide caught up with the cast at the show’s 100th episode celebration and got the scoop on what viewers can expect out of the milestone episode.

The episode is titled “What’s Past Is Prologue,” and it will feature Barry and Nora going back in time, as part of their plan to stop Cicada. Check out the official synopsis below.

In the 100th episode, Barry and Team Flash come up with a plan to stop Cicada. However, the plan calls for Barry and Nora to travel back in time to gather some key necessities. Barry hesitates, concerned about his daughter seeing certain parts of his life. Meanwhile, Sherloque Wells takes his concerns about Nora to Iris, as Caitlin turns up a key asset in the fight against Cicada.

READ MORE: The CW To Simulcast MTV's VMAs On Sunday, September 12 At 8 PM

Jessica Parker Kennedy, who plays Nora Allen in the series, explained an important moment that her character witnesses when she travels back in time with her dad.

“She gets to see a moment, a really special moment where her mom is comforting Barry in this way that like really breaks her heart,” Parker Kennedy said.

READ MORE: Cristela Alonzo Set To Host The CW's 'Legends Of The Hidden Temple'

“She gets to see Barry and Iris as we’ve known to love them over the past four seasons… It’s really nice, I think, for Nora to see the romance between her mother and father and why they are so in love.” Parker Kennedy’s on-screen mom, Candice Patton [Iris West], elaborated.

Of course the episode isn’t just full of happy, touching moments. Nora will also see some ugly situations and realize that while her dad is a superhero, he isn’t perfect. Despite the difficult memories, Parker Kennedy thinks there’s a lot of good that comes out of the episode for the West-Allen family.

“Ultimately, the 100th episode, even though she finds out awesome stuff about her mom, not so awesome stuff about her dad, the episode really brings the three of them closer,” she explained. 

MORE NEWS: July Season Premieres & Finales

The 100th episode of The Flash will air Tuesday, Dec. 4 at 8 p.m. on The CW Philly.