You enter a room. Four heavily armed agents whip around, focusing their sights on you instantly. They're going to shoot any second now, unless you react quickly. What do you do?

In the majority of shooters - the majority of games in general, really - the answer would be simple. You shoot back. You're the hero, after all, so you automatically receive the most weapons, the most ammo, the most armor and the most health. You're an unstoppable, trigger-addicted tank.

Mirror's Edge is different. Really different. As Faith, a foot messenger working for the underground in a futuristic metropolis, you don't usually carry a gun. It's not in your job description. You certainly can't carry anything powerful, as the weight would slow you down. In fact, because you need to move fast at all times, you're much more agile and flexible than you are big or strong. You can't fight back... not in the usual way. So what do you do?

You run. You turn your back on the guards, exit the way you entered and run for your life. Welcome to a whole new genre - the first person runner. Don't worry; it looks a hell of a lot more exciting than it sounds.

See, Faith is trained in parkour, the amazing and relatively new art of free running (go here for video). She can do more than sprint. She can slide under pipes or leap over fences without losing speed or momentum. She can grab onto walls as if they had handles and scale ledges as if they were ladders. She can launch herself off a building's edge, fly across a dizzying gap and land on the next building's rooftop with no injury and absolutely no special equipment. She's part Spider-Man, part Prince of Persia.

As the player, your goal is to guide and control that unique movement. Faith can't lose momentum, so you must study the environment carefully, anticipate obstacles in advance, remember to soft roll after every jump and watch for scalable objects (highlighted by the game in bright red). Build up an uninterrupted flow and you gain "reaction time," a sort of "bullet time" that slows everything down and enables crazier stunts. As Faith runs, you'll even be able to see her body reacting to the surroundings. Her feet pound the pavement, her legs curl under her during a slide and her hands grasp for holds. You can hear her breathing rate increase and catch fleeting glimpses of her face in the mirrored skyscrapers of the city.