The developer behind the adventure fitness app Zombies, Run! is back with another similar title – The Walk. Six to Start and Naomi Alderman have teamed up with the U.K. Department of Health and NHS to create the interesting app.

As the game starts, a bomb explodes inside a railway station. Gamers are given a package that could save the world. But to stay alive, they’ll really need to start walking.

During the day, walkers progress through the game, unlocking audio story clips and other mysterious clues that help solve the puzzle. The game takes around three months to finish and is composed of more than 65 episodes and 800 minutes of audio.

Instead of giving walkers a specific goal, like 10,000 steps per day, the app’s difficulty changes based on data it gathers about the player’s fitness level. Ultimately, the app is designed to keep users healthy by getting them to be more active.

Along with offering a new, battery-saving motion tracking technology, The Walk is also designed to take specific advantage of the M7 motion coprocessor in the iPhone 5s. Users of Apple’s latest handset will be able to have their steps counted with a very small amount of battery usage.

Designed for the iPhone/iPod touch, The Walk can be downloaded now in the App Store for $3.99.

I’m interested to try out The Walk. Unlike wearable fitness trackers, the game structure gives players some definite goals to reach while getting more active.

For other app news today, see: Spotify Mobile Free Officially Launches To Take On Apple’s iTunes Radio, Holiday-Themed Surprises Await In The Simpsons: Tapped Out’s Latest Update, and Rovio Celebrates Angry Birds’ 4th Anniversary With New Birdday Party Levels.