TV

Actor brings double dose of creepy to ‘The Following’

Thanks to British actor Sam Underwood, television has a new baseline for creepy serial killers.

Underwood joined the Season 2 cast of the Fox hit “The Following” Sunday night with a scene-stealing part that teeters between downright disturbing and humorously horrifying.

[SPOILER ALERT] Underwood portrays identical twins Luke and Mark, who use murder to keep the memory of presumed dead serial killer Joe Carroll (James Purefoy). Underwood’s performance — think Patrick Bateman from “American Psycho” meets Norman Bates from “Psycho” — pushes the show away from its FBI procedural roots and into quirkier territory. And he is happy to play along.

“(Creator) Kevin Williamson has done a really good job of writing very sick stuff,” Underwood said, laughing, during a recent interview. “There is a lot of dark, messed up humor that is so fun to play with on set.”

Underwood, 26, enters the series as Luke, whose bedroom eyes and disarming grin seduce a young woman named Heather in her New York apartment’s lobby. In a disturbing montage, Underwood’s character then engages in post-coital banter (including an offer to make breakfast) with a very-dead Heather on her bed. Most disturbing, he slow dances with a limp-bodied Heather as England Dan and John Ford Coley’s 1976 ballad “Nights Are Forever Without You” swells in the background.

Underwood’s dual role is revealed only when Luke emerges from a bathroom shower to stand next to Mark in a scene that likely prompted viewers to hit their DVR’s rewind button, looking for visual clues to distinguish gregarious Luke (the dancer) from reserved Mark (the pillow talker). Hint: Luke favors slicked-back hair; Mark has bangs.

Playing a freak isn’t entirely new ground for Underwood. The charming native of Surrey, England, was Dexter Morgan’s young protégé, Zach Hamilton, on the final season of Showtime’s “Dexter” last year.

“I felt like I was playing with the big boys from the get-go. Once I kind of got over my initial ‘wow’ factor, it was an absolutely joyous experience,” he says. He also played Leo Carras, the troubled boyfriend of Nicolas Brody’s institutionalized daughter Dana (Morgan Saylor), last season on Showtime’s “Homeland.”

Only a few years ago, self-professed “song and dance guy” Underwood seemed destined for disciplines other than horror.

After college in the UK, Underwood moved to New York in 2006, where he enrolled at the American Musical and Dramatic Academy. On a personal blog from 2008, he proclaimed that he was “Following the American Dream, Pounding 42nd Street to be in a show!”

He landed gigs that included touring with the company of “Seussical” in 2008. In 2010 alone, he performed in the Irish Repertory Theatre’s 2010 staging of “Candida,” joined Alec Baldwin for the East Hampton production of “Equus” and cofounded the Fundamental Theater Project, a company that fosters cross-cultural collaboration. “I’ve been very, very lucky to do a little bit of everything,” he says.

Now Underwood’s savoring his shift to television and impressing those around him, including series star Kevin Bacon, who plays former FBI agent Ryan Hardy. “I love Sam Underwood’s character and the way he fearlessly embraces it,” he says. “I was talking with James (Purefoy) the other day, saying sometimes you gotta go big or go home when it comes to playing these people. But I think Sam also plays it with a lot of subtlety.”

Williamson, who says Underwood’s audition “blew us away,” gives him high marks for his fluidity.

“He’s acting with a stand-in when he’s doing the twins. But then he goes and plays the other part — and he’s acting against the performance he just gave you, not the stand-in,” Williamson says. “You put it on the computer, he watches the playback and then he goes and acts with his imaginary self, from memory. It’s really quite wild.”

Underwood is more humble about the talent required. “When going between characters, there’s a certain amount of, like, psychological stamina to go into a literal flip of mind set because you’re thinking of someone else. But for me it’s just a lot of fun,” he says. “I know it sounds like I’m dodging the trials and challenges of doing it, but I’m sure the challenge from the split-screen comes from the technical department more than me.”

However, Underwood recognizes the role is a series — and personal — game-changer. “The stakes are very high joining the second season on a show that just got such great ratings last year. The greatest thing is that there’s not a lot of TV characters that are like this right now,” he says. “It goes back to the idea of having fun with it. They’re both incredibly sick and twisted — though with a lot of humor.”