Zombies, Run! is one of the most inventive games to have been released for smartphones in recent time: a fitness app that encourages players to run with a storyline based on slavering zombies chasing them.

Developer Six to Start says the app has sold more than 300k copies on iOS, Android and Windows Phone – impressive considering it’s a paid app that’s never been cheaper than $1.99. Now it’s getting an episodic ‘second season’.