Zo In-sung on his 'Humint' co-stars: 'Park Hae-joon was the one who scared me'

Three films deep with Ryoo Seung-wan, and Zo In-sung still describes the director in exactly the same terms: razor-sharp, relentless, incapable of talking about anything other than movies.

"He's exactly the same every time. Locked in and completely wired," Zo says at a cafe in Samcheong-dong, Seoul, on Wednesday. "Even the small talk is about film. That's all he knows."

Their latest collaboration, "Humint," pits Zo's South Korean intelligence officer against Park Jung-min's North Korean operative across Vladivostok, with Shin Se-kyung and Park Hae-joon rounding out a loaded cast. Production spent months in Riga, Latvia, standing in for Russia's far eastern port city.

Working out the fight choreography with Park Jung-min was the easy part, Zo says -- they'd already built a rhythm across their previous work together in "Smugglers." The foreign stunt crews were another story.

"The overseas teams had a very different style," he says. "Their fists would come right up to your face. There were moments I genuinely thought, wait, is this guy actually gonna punch me?"

When it came to the ensemble, Zo reserved his highest praise for Park Hae-joon (the bullheaded, devoted husband of "When Life Gives You Tangerines"), who plays the oily consul general pulling strings behind the scenes.

"He's the one who really got to me," Zo says. "The way he just drops all the pretense, lets it all go loose, and somehow that's what makes him terrifying. You can't tell what the guy's thinking.

"He doesn't announce himself as the villain. He just is who he is. Hae-joon deserves more credit than he's gotten for that performance."

Of Park Jung-min, currently the hottest name in the Korean film industry after a show-stealing performance at last year's Blue Dragon Awards, Zo sounded like someone who saw it coming a long time ago.

"Jung-min was always up for it. I watched him grow, and it was obvious he'd blow up," Zo says.

Whether by design or by accident, Zo's own role in the ensemble functions less as a conventional lead than what he calls a "bass"-- the low-end frequency that holds the track together while the kicks do the flashy work.

It's a metaphor he returns to more than once, and one that says as much about where he's headed as what he did here.

"You can pile on all the kicks you want, but without a solid bass, there's nothing holding it up," he says. "A lead is like air. You don't notice it when it's there, you're breathing it all the time. But take it away, everything falls apart."

That's how he approached the job this time around, not so much the center of attention as the thing keeping everyone else in orbit.

He occasionally pitched ideas to Ryoo on set, flagged moments where the relationships between characters needed tightening, trying to give the director one less thing to worry about.

"Being the person others lean on and being the person who gets to lean on someone, those are very different things," Zo says. "This time, I had to be the former. It's harder than it looks."

"Humint" is now in theaters.