We all know the story. Patient Zero appears mysteriously and the world is infected with the zombie virus, leaving few intrepid human beings behind to band together and simply stay alive. Resources are few, hope is low, and the world is quiet.

Zombie apocalypse narratives have become a hugely popular part of the cultural canon in recent years. From 1968’s Night of the Living Dead to AMC’s The Walking Dead, something about zombies has captured our attention, and we can’t seem to get enough of them. The narrative, in all its iterations, is infectious. Pun absolutely intended.

But what if you were part of the story rather than a mere observer? What if you had to run—literally run—from zombies to keep your livelihood? Enter Zombies, Run! to the apocalypse scene.

Zombies, Run! is a fitness app cum immersive game that puts you in the role of apocalypse fighter, running for the survival of your township and searching for an end to the zombie plague. The app itself was released in 2012 by London game developer Six to Start and head writer Naomi Alderman after a phenomenally successful Kickstarter campaign. The game proposed simply to make running more fun and is currently in its fifth season of production. You heard that right, season. It’s more than zombies moaning and lurching their way toward you as you run away, there’s a story. A good one.

Boiled down to its essential, you are Runner 5, a crucial member of Abel Township, one of the last remaining bastions of society in England. Each run is a mission, where you’re tasked with gathering supplies, defending the township, and uncovering more and more of the story with every mile. The story itself is extensive, with an entire cast of characters, enemies, plot twists, and some downright unnerving sound effects that would motivate just about anyone to get moving a little faster.

I spoke with Naomi and CEO of Six to Start Adrian Hon, both of whom are hard at work on season five. With over two million downloads, the game has both a tangible impact and intrigue, not to mention an awful lot of moving parts. In four seasons, the app has gone from an engaging audio adventure to a full-blown fitness app—GPS maps, stats, calorie tracking, variable run times, you name it. And while all of that is engrossing for a fitness nerd like me, the reason why I keep coming back is the story. I was curious about the general mechanics of the whole thing—radio dramas are as old as radio itself, but a radio drama piped through running headphones? Set in a zombie apocalypse? Where do you even begin piecing that together?

World building is an effort no matter what medium you’re working in, but what were the elements you wanted to incorporate into this world?

Naomi: In a way, my job was easier than many world-building tasks, because the idea of the zombie apocalypse is already well embedded in our culture. So I didn’t have to explain what a zombie was, or how they operate, or what the world might be like a while after a zombie apocalypse has happened. I wanted to make an apocalypse in which it’s not all about guns and suddenly everyone is a cannibal, but maybe we do better pooling resources and working together than we do using rugged individualism to gut our way through. It’s a kinder—but dare I say it, a more realistic—apocalypse.

What do you have to take into consideration when writing for this non-traditional, app-driven, audio-focused format? How do you keep a player, who is in the middle of a physical activity, engaged with the story?

Adrian: It turns out that’s really hard to do. The story only really works in the sense of a role-playing game if you’re running and the character’s running. So why is the character running all the time? Even James Bond doesn’t run all the time. That’s actually why we did a zombies game. It’s not because we love zombies, it’s because that is a great scenario to explain why you’re running all the time.

Naomi: [We have to] make the running feel worth it. You can be running because of something funny, scary or sad, something that makes you feel angry or determined or vengeful but it always has to be something worthwhile. We’re asking a lot from our players—most games don’t ask you to sweat and get out of breath for 30 minutes—so it’s our job to make sure the player feels they haven’t wasted their time. If we do it right, the thought hey I got some exercise! should be a nice bonus to I stopped those zombies eating those schoolchildren.

Adrian: Naomi’s scripts are great, and I always chip in with ways to make it more like an action movie, but if we did that all the time it would be a bit one note. We mix this great character development, great plot, with really exciting moments where your house is falling and jet planes are coming overhead and that sort of thing.

How do you get the player to inhabit the character of Runner 5, who cannot speak?

Adrian: Naomi would tell you that the character would always do what a reasonable and intelligent person would do. So we never have Runner 5 being stupid, and the character is always loyal to the people in the game, Sam and Janine and the rest. The other thing is that you set up situations where it’s obvious what the right thing is to do.

Naomi: I never want to put the player in a position where Runner 5 does something and they go “but I would never do that!” Which involves some fancy footwork in the writing. The archetypal example of course is: there are zombies behind you, you have no weapons, what are you going to do? Run!  In addition, we always make sure that Runner 5 is completely gender-neutral. It’s a matter of some pride to me that in more than 200 episodes there’s not a single gender marker for Runner 5, or any other marker of race, ethnicity or anything else. We never want the player to feel like “hey, that’s not me!”

Adrian: Zombies, Run! is not a traditional video game. It doesn’t have the same kind of interaction, but if you compare it to silent protagonist games like Half-Life and Portal— You don’t have a choice in any of those games, and you never say anything either. They work because they’re disaster movies; it’s obvious what you should do. You’re trying to survive and get out. Zombies Run! works because you have this voice in your ear. You have Sam, who you can always trust. So we share a lot of DNA with Half-Life and Portal and we’re helping the player understand what they’re meant to do.

Can you speak to the notion that you get to “be your own hero” with Zombies, Run! and how that ties in with the physical activity associated with the storytelling?

Naomi: Exercise has always been something I have to consciously decide to do. I think it’s that way for a lot of people. So it was always important to me to make a game that rewarded the players for the sheer fact of getting some exercise, rather than did you go harder/faster than last time? or did you beat your buddy? I couldn’t care less about who I’m better or worse than, the critical thing is that I do actually move my body most days. So I wanted Zombies, Run! players to know that they were a hero every time they went to get some exercise. That we’d never say “you’ve failed”—if you’re moving, you’ve succeeded. Even if the zombies catch you while you’re running, you don’t fail the run! You just drop some virtual supplies and carry right on.

Adrian: People have emailed us saying that the game has saved their lives. Just the other day I saw someone claiming that we saved their life, that they lost 100 pounds because of Zombies, Run! We have never made a claim that this game will— we just make running more fun.

Naomi: When you’re Runner Five, you’re a hero. No matter how much you weigh, or how you’d like to be in better shape than you are, no matter whether you’re injured or have a disability, no matter how fast or slow you go, you’re Runner Five and Runner Five is a hero.

Zombies, Run! is available for iPhone and Android.