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Mark-Paul Gosselaar stars as Brad in Fox’s “The Passage,” which airs Season 1, episode 5 on Monday. Erika Doss / Fox

Episode 5 of Fox’s TV show adaptation of Justin Cronin’s novel series, “The Passage,” airs Monday, and fans of the book will be treated to yet another familiar character.

Horace Guilder (James Le Gros), known in the book as the Deputy Director of the Department of Special Weapons, arrives in the new episode, with the synopsis currently describing him as a “high ranking official.”

“That’s the beauty of what [creator and executive producer Liz Heldens] has done… there’s characters that are in the books that are beloved and she inserts them in a new way but still keeps the roots the same,” Mark-Paul Gosselaar, who plays Brad, told International Business Times at New York Comic Con last year. “It’s kind of fantastic what she’s done. Guilder comes back, and all these characters. I’m like, ‘That’s Guilder from the book!’ He’s working in episode 5 right now. So, that’s fun.”

Guilder’s debut wasn’t the only thing the actor teased about Season 1, episode 5 of “The Passage.” He also shared “this is probably the most ambitious show” he’s ever been a part of, and a scene from Monday’s broadcast is a prime example of why.

“We spent nine hours on one action scene where Brad meets a viral and [it’s the] first time watching a viral move and how they attack and all that stuff,” Gosselaar told IBT. “Not to give too much away, but we spent a lot of time. And that’s something on television shows we don’t have the luxury to do, but, on this, I’m glad they’re giving us that time because I think it’ll really translate onscreen, and fans will appreciate it.”

Up until now, viewers — and the show’s characters — have really only seen the virals inside their glass cages. That’s about to change in the new episode, titled “How You Gonna Outrun the End of the World?,” when one of them shows off their unique viral movements.

According to the Season 1, episode 5 synopsis, here’s what else you can expect to see during the broadcast:

“With the sudden arrival of a high ranking official, Horace Guilder, to Project NOAH, Brad and Amy [Saniyya Sidney] begin to strategize a possible escape plan with the help of an unlikely accomplice. Meanwhile, Sykes [Caroline Chikezie] and Richards [Vincent Piazza] begin to question each other’s motives, and a shaky past between Lear [Henry Ian Cusick], Elizabeth (Jennifer Ferrin) and Fanning [Jamie McShane] is revealed.”

“The Passage” airs on Fox on Mondays at 9 p.m. EST.