It's just you and a grapple gun, trapped in 22 levels of cuboid puzzlement. Reach a teleporter to escape each level, pick up the access codes along the way, avoid electrified panels. The trick is to use your grapple gun to hook onto the green areas dotted tactically around levels. Sometimes you'll be jumping into an apparent abyss, often there are switches, the platforms hardly ever stay still and precision timing is all. Which can be frustrating.