Matt Osterman's sci-fi thriller 400 Days is difficult to talk about in detail without venturing into spoiler territory. It begins with a group of aspiring astronauts - played by Brandon Routh, Caity Lotz, Ben Feldman and Dane Cook - resigning themselves to over a year spent in an underground facility designed to simulate the psychological effects of deep space travel. They are sealed in, the countdown begins, and it isn't long before things begin to go awry and a mystery arises: while they have been inside their spaceship, what has been going on outside?

The Flash star Tom Cavanagh plays Zell, a character who may be key to answering that question and is therefore especially difficult to talk about without giving away too much about the plot. Screen Rant got a chance to speak to Cavanagh ahead of 400 Days' release, to get his (spoiler-free) take on the movie and tease what audiences can expect to see from his character.

What was the appeal of 400 Days for you? Was it something particular in the script that made you really want to do the movie?

I read three movies in one day. [Laughs] Not like that’s a typical day when you get like three movie offers. But I read the first one and I’m like, “Oh, I’m going to do this. This is great.” Then I read the second one... The second one was even better and I was in every scene... “Oh, this is going to be great. I’m going to do this one.” Then I read 400 Days... and it was like a no-brainer. I was like, “Oh, absolutely this one.”

And it’s funny, because in terms of screen time, it’s a much smaller part. But the thing I liked about 400 Days was it was so psychological, sparse… just the landscape of it I thought was really intelligent. It’s evocative of…the old Twilight Zone episodes... The idea where you kinda ask the audience to inject their own opinions into it: “Is this pit, is this supposed to be hell?” You know, that kind of thing. The darkness, is that him being overcome by his demons? Is that what the dark represents? All this kind of stuff that Twilight Zone did with very little effects, this movie kind of reminds me of that.

It’s a very simple conceit, essentially. You know, these people are being prepped for deep space travel by being put in a simulator to see if they can handle it for 400 days. So it’s simple. But then, the question that rears its head is: Is it really a simulation?

You have an interesting role. I didn’t really know anything going in... So I kept wondering when you were going to show up. It was like, “There’s just four people in here!"

Yeah, you’re right, like, “He’s not in this movie!”

“Have I got the wrong movie or something?”

Yeah, exactly.

We don’t really know much about your character when we first meet him. And even by the end of the film there’s still lots of gaps in what we know about Zell. Did you have additional backstory or did you come up with your own backstory for the character?

I don’t want to give away too much of the movie, but having seen it you’ll know what I’m talking about. I sort of… borrowed is probably a generous word. I stole from the old Westerns. You know, the idea of the straw that stirs the drink, the standing man in the small, small cowboy town... You don’t know too much about him, but clearly he’s at the center of the town, although no one ever really says why he is. But you just get the sense that this man is an important figure in this town. He’s like the dark lone gunman of some cowboy town.

What one item would you bring along to help you pass the time for 400 days?

That’s a great question. I love that question, which you just, by the way, sprung on me. So I don’t know. [Laughs] I certainly think it’d be, you know, maybe… Oh, boy. It’d be tough to… Have you see The Martian, by the way?

Yeah.

So it’s the same sort of idea, right? That central conceit is like, “OK. You’re the guy. Use what you got.” It drives him crazy, but you feel there’s a certain symbiosis there, too, where he also depends on it, because you need music. It drives him crazy in The Martian. Spoiler alert for people out here who haven’t seen or read the book! But it drives him crazy that he is forced to listen to the only available music, and that is disco. He just got to listen to nothing but ‘70s disco music. I think having a wide flung musical cannon would be… I don’t think there could be something much more valuable than that if you were stuck in deep space.

It’s interesting. I was speaking to Caity earlier and she said the exact same thing. She said she’d bring along music - but probably not disco, I don’t think.

Oh, really? That’s great.

Between 400 Days, The Martian, Interstellar, Gravity... There does seem to be a renewed interest in the film industry in space travel movies...

It’s funny. When he did Gravity, the director… was asked on its release… I believe it was at Cannes that this question was asked. The question was: "What it’s like filming in space?" [Laughs] There’s just like a big long pause while he stares at the questioner.

But you kinda can’t blame the questioner for asking it, because that’s exactly what it looks like. The digital and technical investments of today have allowed directors to make composed shots and make movies that, indeed, look like they were filmed in space... I think nowadays it’s easier to put the things in that you imagine in your head and put it down on screen. Moreover, it’s also not as expensive, prohibitive as I think those imaginings might have been in the past.

400 Days was produced by Syfy, so it makes sense to assume it’s sci-fi. But depending on your interpretation of the film, would you consider it a sci-fi film? Would you consider it kind of more of a psychological horror... or maybe a Western?

You know what I consider it? I think the best heading for me… I’m not the guy to really offer any kind of expert opinion on it, but I would call it a suspense film. I remember watching…All those designations could have been applied to Alien the first time I saw Alien. But I remember thinking: “This is possibly the best suspense film I’ve ever seen.” They are in deep space. It’s sci-fi, clearly… It’s a space film. But, ultimately, there’s something out there that wants to kill them, and where the hell is it? They can’t move. They are in contained spaces they cannot get out of and there’s something lethal hunting them. There’s something awful after them. You didn’t even reveal what that thing was until three-quarters of the way through the movie. You just kept hinting and guessing and showing and pushing and grimacing. But you never really saw the full iteration of it until…

You didn’t need to have the monster mashing around and seeing the whole thing and destroying a town. It was like six people out in space and they had nowhere to go. And you didn’t even really get a good look at what was after them. But it was like an incredible cocktail for suspense. I thought it was one of the best things I’d ever seen.

I am not equating 400 Days with that kind of… That’s a movie that’s in the pantheon. And that’s the place we’re all trying to get. But I think that the designation applies in the “What the hell is going on here?” And that hopefully makes 400 Days a suspense film, and hopefully a good one.

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400 Days is available now on VOD and limited theatrical release. Check out the trailer below.