Spoiler alert: This piece contains spoilers for Part 1 of Season 4 of “Ozark,” currently streaming on Netflix.

As “Ozark” barrels toward its bloody conclusion, the drama series introduced a new and terrifying antagonist for Marty and Wendy Byrde (Jason Bateman and Laura Linney), the money-laundering couple at the center of the show’s criminality and carnage. They make work for Omar Navarro, the coldly calculating leader of the Mexican cartel that has made them rich, but also in constant danger of losing their lives. But it’s Omar’s nephew Javier “Javi” Elizondro who may pose their greatest threat.

A business school graduate, who thinks nothing of personally dispatching civilians, enemies or even unlucky local sheriffs, Javier is ruthlessly ambitious and in a hurry to climb to the top of the cartel ladder. Portraying the Byrdes’ nemesis fell to Alfonso Herrera, a Mexican actor who previously appeared on Netflix’s “Sense8” and Fox’s “The Exorcist.” He figures to factor in prominently during the second half of “Ozark’s” final season — Netflix has split Season 4 into two seven-episode parts — when it premieres later this year.

In a spoiler-filled conversation (seriously, stop reading if you aren’t caught up on “Ozark”), Herrera spoke to Variety about bringing Javi to terrifying life and why he may be on a collision course with Marty, Wendy and anyone else who would stand in his way.

What’s the secret to playing Javi?

When I read the script, I realized that I needed to find and enhance those little moments where Javier is unpredictable. And there are other qualities to Javier. He likes simple things. He likes to enjoy things. But most important, he never lies. He is very straightforward even though everyone around him is lying and covering their tracks and hiding what they’re really trying to say or what they think. If he doesn’t like you, he will tell you. If he doesn’t like his uncle’s approach, he’s going to let him know.

In one of your final scenes you brutally murder Darlene Snell (Lisa Emery) and Wyatt Langmore (Charlie Tahan), two fan favorites. What was that like to shoot?

It was tough. I remember when I started watching “Ozark,” Darlene was one of my favorites. When I arrived on set, it was the first time I was meeting Lisa. We locked eyes. She looked at me and I looked at her, and she came up to me and told me this was going to be tough. And I didn’t really know what to say other than to tell her that it was an honor to share a set with her and be part of such an amazing and important part of the story. All the crew was sad because they were saying goodbye to a character that had been there since the beginning and at the same time they were saying goodbye to an actress who had done such amazing work.

How is Javi different from his uncle?

Javier wants to build something bigger and more modern. Omar has run his business in an old school way. Javier is not afraid of burning bridges to accomplish what he wants to accomplish and Omar is trying to say farewell to that life. He wants to step away and make a deal with the U.S. government. Javier wants to be seen. He wants to make a mark. That’s why he’s so aggressive.

In the last episode, Javi seems to be holding all the cards. Omar has been arrested and Javi has agreed to become an FBI informant, which basically indemnifies him as he consolidates power. How will that change him?

He’s aware of the power he has now and that makes him more comfortable in his skin. There’s an aura to him that’s scary. That’s going to be very interesting to see work out in the second part. It’s going to be interesting to see how he reacts to other characters. And we’re going to see the relationship he has with his mother more fully. It is presented in a very small proportion in the first part of the story and it’s going to be a lot clearer and more important in the second part.

Javi tells the Byrdes early on that he thought Omar should have killed them. What’s his relationship like with Marty and Wendy?

It’s very clear since the first episode that he had a very different point of view in terms of how he wanted his uncle to handle the Byrdes, so it’s a struggle with them in terms of navigating their relationship with Omar. In the second half of the season, he’s going to be a huge headache for the Byrdes, for Marty and for Wendy.

Have you finished shooting the entire series?

Yes, we shot everything. All fourteen episodes are in the can.

So you know everything that happens? Are your friends and family harassing you for spoilers?

Of course. Everyone is sending me texts and emails asking me what’s going to happen. The only thing I can tell them is prepare to have your mind blown. The creators saved the best for last.

This interview has been edited and condensed.