LONG BEACH, Calif. – In “Dexter: Original Sin,” Patrick Gibson portrays a younger version of the infamous vigilante serial killer, surrounded by a stellar cast including Christian Slater, Patrick Dempsey, and Sarah Michelle Gellar.

During a filming session in September at a dusty gypsum warehouse near Long Beach, the 29-year-old Irish actor found himself awestruck by a silent stuntman acting as a gruesome murder victim lying in the dirt.

Wearing gloves, Gibson (“Shadow and Bone”) depicts Dexter as a rookie police forensics intern, methodically pulling a plastic bag from the victim’s head, exposing ghastly eyes.

“It was the dirtiest place I’ve ever worked,” Gibson remembers. “At one point, I accidentally dumped a pint of dust on the actor’s face and open eyes. Remarkably, he didn’t react at all. I thought, ‘This guy is probably the best actor I’ve ever collaborated with.’”

“Original Sin,” streaming Fridays on Paramount+ and Sundays on Showtime at 10 EST/PST, will require numerous standout performances for the origin tale of Dexter Morgan—a blood-spatter analyst with the Miami Metro Police Department who secretly hunted criminals as a vigilante killer. This role, previously played by Michael C. Hall in the original series from 2006-2013, set the stage for a new serial killer, who has left another body behind in this fresh storyline.

“I just learned Dexter had taken out 149 people in his lifetime,” says Gibson. “That’s a pretty impressive tally, especially considering he never got caught.”

Those killings occurred while adhering to the strict Code of Harry, established by Dexter’s father (played in flashbacks by James Remar), who recognized and guided his adopted son’s “Dark Passenger”—a term for his murderous impulses. Dexter only targeted proven criminals guilty of murder to quench his thirst for violence. He also meticulously covered his tracks, wrapping victims in plastic to ease cleanup.

With a cop’s haircut and a serious demeanor, Slater, 55, who plays a younger Harry Morgan, advises the budding detective to be discreet about his serial-killer knowledge while investigating the crime scene.

“But Dexter was destined to do what he does,” Slater notes while relaxing in his trailer between filming sessions, wearing compression socks with his soiled shoes left outside. “If not for Dexter Morgan, there would be many more serial killers roaming free. We simply don’t hear about them because Dexter took care of that problem.”

Set in Miami during 1991, “Original Sin” uncovers graphic crime scenes and reveals Dexter’s upbringing with his father Harry and his sister Debra (Molly Brown). In the original “Dexter,” Debra (played by Jennifer Carpenter) protected her brother’s secret life, but in their teenage years, they navigate typical sibling rivalries and share breakfasts amid a backdrop of catchy ’90s pop tunes.

“We’ve never seen these characters in a home setting,” Gibson explains. “They come across as a seemingly normal family, full of smiles.”

“Original Sin” also reintroduces beloved figures like the beloved cop Angel Batista (James Martinez) and key behind-the-scenes players, including original executive producer and writer Clyde Phillips. Surprisingly, Hall returns as Dexter, who was killed off at the close of “New Blood.” Interestingly, Hall will voice his younger self’s inner thoughts during a critical scene from an operating table in “Dexter: Resurrection,” set to premiere on Showtime next summer.

Christian Slater and Patrick Dempsey reunite on ‘Dexter’

Slater is depicted as part of the Miami metro police force alongside Capt. Aaron Spencer (played by “Grey’s Anatomy” star Dempsey) and CSI Chief Tanya Martin (played by “Buffy the Vampire Slayer” star Gellar). The reunion between Slater and Dempsey carries a nostalgic weight, particularly since they had a heated rivalry during the filming of “Mobsters,” which was a box-office failure in the same era as their new series.

“That was over 30 years ago; we were youthful and competitive,” Slater reflects. “It was quite intense. Now, we’re friends and both settled with families, waking up early for our kids.”

They make each other laugh on a daily basis.

Christian Slater, known for his role as a high school sociopath in the 1988 film “Heathers,” expressed surprise when he received the call to portray the mild-mannered character Morgan.

However, Morgan has more layers than initially apparent, having been revealed to have died by suicide in Season 6 of “Dexter.” “There’s a troubled history there. One might question, ‘Does Harry have his own Dark Passenger?'” Slater muses with a raised eyebrow. “I truly think he does. But (Gibson) certainly finds himself in far more sinister scenarios – lurking in murky waters disposing of bodies.”

In fully embracing his character’s Dark Passenger, Gibson sheds his Irish accent and chillingly adopts the emotionless tone of Hall’s Dexter. His dedication to preparation is such that he often listens to his lines on AirPods while on set and during breaks.

“I’ve binge-watched ‘Dexter’ more than any other series, focusing on details like Dexter’s unique lip wipe,” Gibson shares. “He has a distinct physicality. It’s fascinating to think about how he would have moved 15 years prior.”

Known affectionately as Paddy, Gibson has a boyishly charming appearance and became an internet sensation in June when he announced his relationship with “Euphoria” actress Maude Apatow through an Instagram photo featuring a sweet kiss courtside at a Knicks game. Despite his charm, he often finds himself cast in darker roles, like a drug-dealing student in Netflix’s “The OA.”

“For some reason, I often portray quite a few not-so-good characters,” he jokes with a smile, making it clear it’s taken lightly. “Perhaps that’s when I can truly express myself and find comfort in a kill room.”

Gibson realizes that portraying a killer is much preferable to lying lifeless in the dirt with a plastic bag over his head. “What I’ve come to understand,” he states, “is that I genuinely prefer being the killer rather than the victim.”