Douglas Smith has been making the most of a golden opportunity.

Smith is about to make his return as Marcus Isaacson, the more extroverted of the twin forensic crime-scene pioneers on The Alienist: Angel of Darkness, which debuts at 9/8c Sunday on TNT.

Two episodes will air on the next four Sunday nights on TNT.

In this chapter, Sara Howard starts her own private-detective agency. She gets hired to locate the kidnapped infant daughter of the Spanish consular. And the band is soon back together.

Smith, 35, has a look that makes it hard to peg his heritage. In an exclusive interview, Smith admits to be uncertain himself.

“I struggle with what my identity is,” he said. “I've got an English father and an American mother. They got together and had kids in Canada. My Canadian friends refer to me as American, my American friends refer to me as Canadian. My father always tells me I'm English. So I don't know.”

Smith's most recent TV appearance was starring as Corey on the second season of HBO's Big Little Lies. Among his other TV roles are starring on Big Love, appearing on the miniseries When We Rise, and recurring on Vinyl.

Smith as Marcus and Matthew Shear as Lucius play the important role of science geeks on The Alienist, providing some light moments on a very dark show.

Star Daniel Bruhl, who portrays the titular alienist, Dr. Laszlo Kreizler, refers to the duo as Thomson and Thompson, after the comedic bobbies in the Tintin series.

“That's the best part of the show,” Smith opined. “I'm very happy every time I get to act opposite Matthew Shear. We come into scenes with a lot of energy, a lot of ideas. I like being able to change up the pace at which the show is going. The brothers will come in with their scientific experiments and their sometimes intelligent ideas.”

The Isaacsons were experimenting with forensic techniques of the era, some of which haven't held up well.

“Looking at it from the perspective of 2020, we can see some of their ideas as being hocus-pocus,” Smith explained. “But the fact that the Isaacsons are interested in [cutting-edge techniques] shows they are reading the [scientific] journals of that time. Matt and I brought a lot of books and we'd sit at the cafe and talk and talk and talk.”

The Jewish Isaacsons couldn't help but be outsiders within the Irish good-old-boy network of the NYPD.

“It was a fun dynamic to play dealing with the antisemitism coming from the Irish police,” Smith said. “You just have each other. You bind together and play the scenes the way they're written and imbue them with some kind of tension.”

They're a much better fit for Kreizler's team.

“It's a team of outsiders and thinkers as opposed to brute Irish police officers that are walking the beat and just want to beat up anybody and call them the right suspect,” Smith said. “They're trying to think outside the box and analyze things. A lot of the other people at the police department are just bashing skulls together.”

Early in Angel of Darkness, the Isaacsons seem to be gaining some grudging respect for their work within NYPD. Smith cautioned against reading too much into that.

“It's two steps forward, one step back,” he said. “They've given us our little area where we can do our experiments. But [former Police Commissioner] Thomas Byrnes does not really think much about what we do. As the season plays out, there will be building tensions between the Isaacsons and the good old Irish boys.”

Each season of The Alienist took seven months of shooting on location in Budapest, Hungary. This experience drew the cast together.

“All we had was each other,” Smith said. “We were all far away from home, some of us further than others. We grew quite close during the first season and we picked right up like no time had passed for the second season, although there was a significant break between the first and the second seasons. It was nice.”

In its two outings, The Alienist has striking production values. This is beneficial to an actor, Smith said.

“As an actor, it is always preferable when you have physical sets and they're well done, as opposed to walking on to a green screen, for example,” he explained. “I've done one very large production back in the day that was extensively CGI, and that was really, really challenging.

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“Whereas in The Alienist, there are horses running up and down the cobblestone streets. You actually have to watch yourself. So it's cool. It requires less acting, actually, because you're living in the moment, the life of the world that is actually there and tangible.”

Angel of Darkness, based on the second and last Alienist novel by Caleb Carr, was a pleasant surprise for Smith, who learned about it while on a fishing trip with his brother. He's game for another installment should there be interest.

“I think I'm still under contract for The Alienist,” he said. “I think the viewers will really be satisfied after the end of Angel of Darkness. I would like to come back if there's another Alienist novel written by Caleb Carr. I think I read that he was trying to write another novel with this team. That would be the most appealing option to me.”

Dale McGarrigle is a staff writer for TV Fanatic. Follow him on X.