The Girl on the Train spoilers: The killer speaks

WARNING: THIS POST CONTAINS The Girl on the Train SPOILERS.

If you somehow have neither read The Girl on the Train nor seen the movie yet, turn back now! But if you have, and you’re itching for more, you’ve come to the right place. As you’ll know, not only did Rachel Watson’s (Emily Blunt) seemingly long-suffering ex-husband actually kill his former nanny and lover, Megan Hipwell (Haley Bennett) — but Tom Watson (played by Justin Theroux) was also gaslighting Rachel, making her believe she was doing terrible things while blacked out and drunk, when in reality, she was generally either passed out or cowering in fear of Tom’s owntemper.

EW caught up with Theroux — who, in reality, is delightful — to chat about playing the bad guy, and keeping the mystery at bay while still being true to his character’s evil actions.

ENTERTAINMENT WEEKLY: You were very scary at the end of the movie.

JUSTIN THEROUX: Oh good! I hope I am. It’s my job!

That death scene just went on and on!

Oh god, the worst. Poor Haley Bennett — dragging her around the woods. [But] she was trying to trap me!

How did you get attached to play Tom in the first place?

I had just finished my second season of The Leftovers, and came back to a script that was waiting for me. I literally just landed from Austin, called [director] Tate [Taylor] and was like, “I love this script, and I love this character.” It was one of those things that came together so beautifully, and within a few days of being home, I was already in New York prepping. It was one of those fantastic sort of hand-in-the-glove moments that’s just effortless. And also, of course, it was with Emily, and I was like, “Oh my god, that’s going to be so much fun.” It’s weird when everything conspires… you’re with your friend, you’re in New York right after a job ends. It’s just perfect.

What were your thoughts when you read the script?

It’s interesting, when I read the script I was like, “Wow, looks like we’re going to do a lot of night shoots.” And Tate was like, “No no no, it’s largely shot during the day.” And I was like, “What?” Then I went back and re-read it.

It’s a thriller, which, out of habit you think of largely at night, people creeping around the shadows. And there’s something about this suburban story being shot, being told largely in the daytime that’s actually more effective, because everything’s happening at normal times. We don’t have the protection of darkness. But it’s this very blue, gauzy light… The cinematography and the direction was so good, I thought, that it felt like those movies kind of like The Ice Storm, the creepy things that happen in broad daylight.

What kind of conversations did you have with Tate about Tom’s character? What did you want to focus on?

It’s essentially the story of a woman who’s been gaslit. And I love the device of the unreliable narrator, that it’s all sort of wrapped around her addiction of hers, which you’re predisposed to despise her for, even though she may or may not be telling the truth.

So I had to approach it as, “This is a woman who made my life miserable,” even though I had my own flaws — major, glaring flaws in the relationship. But I used her addiction against her in a way that’s manipulative. As far as it relates to Haley’s character, Megan, [the murder is] one of those things that I had to think of as an ordinary guy — who didn’t happen to be that great a guy in the first place — in an extraordinary circumstance. I couldn’t think of him as a mustache-twirling villain. I thought of him as a guy who probably thought it was everyone else’s fault.

Was there anything you needed to understand about him that wasn’t on the page?

I had to think long and hard about Tom and Rachel’s relationship: What it looked like when it was at its best and what it will look like at its worst. Obviously at its worst it’s a chicken-and-egg thing — did he step out on the marriage as a result of her drinking, or was he stepping out on the marriage and it was forcing her to drink. So I did that sort of work, as far as their early relationship. And then what drove him to choose another woman and have a baby. [Tom and Rachel] couldn’t have a child together. Does he blame her?

I always had to think of him as in the right. He was always doing the right thing that was best for him. I didn’t approach it like he was an abusive guy, I approached it like he was a sort of put-upon guy. A narcissist, I guess.

What was your vision of their relationship at its best?

The biggest thing I wanted to know is why didn’t Tom leave the house he shared with Rachel?

I assume he was the purchaser of that house, and it was probably just a move out of stubbornness, also cluelessness as to how his new wife would feel. And he’s also been fired, that was the other thing. I did have conversations with Tate about what his current career status is, and we all agreed that he had probably taken a big pay cut and moved to a lesser firm and is pretty unhappy.

Did you come to any reason why nobody ever met his parents? I just want to know what his deal was!

The deal is, I think he was probably a bit of a quarterback growing up. And then by degrees and by poor choices of his own, everything from his mid-20s on was a step down. Also, it’s just sort of the way that story needed to be told, or the way the book was written, which was not really from his point of view, obviously — because it would have been a really happy story from his point of view!

What was the biggest challenge for you?

I think the biggest challenge was just trying to find the little pick points where you could stay true to the character, but also not betray what had to happen. We sort of threaded the needle with Tate, which was treating two things very differently: Treating his first marriage to his wife as this corrosive, toxic marriage that begat him having to step out of it to be with other women, and then the other thing, [the murder]. Do we think he’s killed several people? Obviously not. He made an extreme choice, which I think is a choice driven by ego and narcissism, to think that you can murder someone and get away with it. And I don’t think he had much guilt around it, you know?